By IGNACIO TORRES, JASMINE BROWN, and ALLIE YANG, ABC NEWS

(NEW YORK) — The last three months have been hell for Vanessa Guillen’s family, in particular her 16-year-old sister Lupe.

“The last 75 days for me, for my family– I haven’t slept,” she told ABC News. “[It’s been] a nightmare.”

Guillen was a 20-year-old U.S. Army specialist who went missing from Fort Hood in April. After months of searching, her body was eventually found.

Her family says months before she went missing, she told them she’d been sexually harassed by a sergeant. They’re still trying to find answers to how this could’ve happened inside one of the largest military bases in the U.S.

Her family is refusing to give up the fight for justice for her death.

“We’re going to be my sister’s voice,” Lupe Guillen said. “She’s going to be heard, and she’s going to be remembered.”

“We are saddened and deeply troubled by the loss of one of our own, Spc. Vanessa Guillen,” the Army said in a statement, adding they are “committed to finding justice for Vanessa and her family.”

Vanessa Guillen had a joyful spirit and was dedicated and loyal, her family said. Marathons were her passion. From a young age, she felt a sense of duty.

Her mother Gloria Guillen remembered Vanessa as a 10-year-old telling her, “‘I’m going to the Army when I am older, I am going to go to the armed forces.”

Her mother remembers not being receptive, but says Vanessa pushed, “‘Si Mami, I am going to go because I want to defend my country, my country,’” relaying the story to ABC News in Spanish.

When she turned 18, she signed up with the Army against her mother’s wishes.

“It made me cry so much that day, all day I cried… I said ‘Don’t sign, don’t sign,” Gloria Guillen remembered. “My mother’s intuition warned me of the pain I was going to feel. My daughter signed.”

The day after her high school graduation in June 2018, she enlisted. First she went to training in South Carolina and Virginia, then in December 2018 she was assigned to Fort Hood in Killeen, Texas — just hours away from her home in Houston. It’s where Gloria and Rogelio Guillen raised their six children and built their American dream.

“I said, ‘Look how beautiful my daughter is,’” Gloria Guillen remembered of meeting Vanessa at the airport. “I hugged her… [she told me,] ‘Because I am happy Mami, I am happy.’”

Then on April 22, Vanessa’s father Rogelio Guillen felt something strange.

“After lunch, after 12 p.m., I felt a strong pain in my chest,” Rogelio said. “Never in my life have I felt something like that.”

He believes the pain was tied to her horrific death.

“It was at that moment when they did that cruel thing,” he said.

Her family says they became worried when she stopped responding to text messages. That same night, her older sister Mayra Guillen went to the base to check in. She says she was turned away and asked to return the following day. That’s when she said she learned Vanessa had gone missing.

“Vanessa was reportedly last seen April 22; concerned about her welfare and unable to establish contact, her unit conducted a search and barracks check. That evening, unit leadership contacted her family,” the Army said in a statement to ABC News. “On the morning of April 23, the unit contacted the military police and reported her missing; later that evening, the Army Criminal Investigation Command (CID) opened an investigation. Also that day, unit leaders met in person with Guillen family members.”

Authorities said she was last seen wearing a black t-shirt and purple leggings in the parking lot of her regimental engineer squadron headquarters. Her car keys, room key, ID and wallet were later found in the armory room where she worked.

“I said, ‘No, tell them to shut down that base. Close that base and find my daughter, for the love of God,’” Gloria Guillen said.

“Since Vanessa’s disappearance, more than 500 soldiers searched for her in throughout Fort Hood while [Army Criminal Investigation Command] agents participated in numerous ground, water and air searches throughout Central Texas,” the Army said in a statement. “CID agents have also conducted more than 300 interviews and are working closely with the FBI, Killeen Police Department, Belton Police Department, Texas Rangers, U.S. Marshals and the Texas Department of Public Safety.”

She says a few months before her daughter went missing, Vanessa told her she was being sexually harassed by a superior but didn’t report it out of fear of retaliation.

“Six months… at the base, my daughter was sad, with bags under her eyes, skinny,” Gloria remembered.

“[Vanessa] told me, ‘I am being sexually harassed by a sergeant,’” she said. “‘Jesus Christ no,’ I said, ‘Have you already reported that bastard?’ [She said,] ‘I haven’t reported him Mami, because they won’t believe me. They laugh at all the girls that have gone and they don’t believe them.’”

Gloria Guillen said she’d offered to report it herself.

“‘Give me the name of that bastard. I am going to report him. I will fight it all,’” she remembered telling her daughter. “‘Mami, I can’t.’ I know why she said she couldn’t, because she swore to defend her country and her homeland. She said, ‘I am leaving, I will fix it, I’m brave.’”

Gloria Guillen never got the name.

The Army said in a statement they are “committed to the reduction, with the eventual goal of elimination, of sexual assault and sexual harassment,” with a goal of “an Army-wide, prevention-focused culture of dignity and respect that fosters healthy command climates in which the behaviors and attitudes that lead to sexual offenses are rare and victims feel free to report without fear of retaliation.”

Since April, the Guillen family has criticized the Army for taking too long to act. The family’s attorney Natalie Khawam has accused Fort Hood of keeping them in the dark.

“When we asked the questions, the real questions, who was with Vanessa that day? Who was she working with that day?… Who called her in? They wouldn’t answer. Who did she work with? They wouldn’t answer,” Khawam told ABC News. “They were just very defensive about it– smirkish about it.”

For months, the family held out hope that she’d be found alive. The search for her continued throughout May and June.

The story of her disappearance gained traction, reaching national news. Dozens gathered at the base to demand justice.

On June 30, two months after Guillen’s disappearance, investigators located unidentified human remains in a shallow grave near a river in Bell County, about 20 miles away from the base. It took days to identify the remains.

“I had to find out from the news that [the remains] were found,” Lupe Guillen told ABC News.

On July 1, 20-year-old army specialist Aaron Robinson, a suspect in her disappearance, died by suicide. It’s unclear at this time how closely Robinson and Guillen worked together, if at all.

According to a criminal complaint against Cecily Aguilar, Robinson’s girlfriend who is accused of helping him dispose of the body, she told investigators Robinson told her he’d “struck a female soldier in the head with a hammer multiple times… Killing her on Fort Hood,” adding that “Robinson then placed her in a box.”

On the morning of April 23, investigators say that Robinson and Aguilar proceeded to “dismember the body ”, “attempted to burn it” and then buried the remains, according to the complaint. Aguilar later stated she recognized Vanessa Guillen as the person inside the box, the complaint said.

While authorities worked to identify the remains, the family continued to seek answers. The agony of Lupe Guillen, the youngest sister, was laid bare for the world to see.

“My sister is a human too. She deserved respect. She deserves to be heard. Because if this could happen to my sister, it can happen to anyone else,” she said at a press conference the day Robinson died.

On July 5, the family received the confirmation they long dreaded. DNA analysis showed the remains belonged to Vanessa Guillen.

“I just went into my room and I didn’t want no one to talk to me. Because I prayed for the– for the past two months… I was hoping for a miracle,” Lupe Guillen said. “I can’t question God why he took my sister. But she’s in a better place. [Vanessa] is that angel that’s going to take care of us.”

Aguilar is now in jail being held without bond. She has pleaded not guilty.

Lupe, only a teenager, is forced to take up this quest for justice.

“I shouldn’t be fighting for my sister’s life — no one should. Especially if it’s on a military base where you think everything’s safe. Yet my sister was not safe,” she told ABC News.

Allegations surrounding Guillen’s death are shining a bright light on what critics say is a systematic problem in the military — that sexual harassment and assault is downplayed and there’s a severe lack of accountability for misconduct.

Now, demonstrators are taking to the streets with signs emblazoned with Guillen’s name. Thousands have flooded social media with #IAmVanessaGuillen to share their stories and outrage.

The League of United Latin American Citizens (LULAC) has urged women, “especially Latina women” to not enlist in the military “until we have assurance they will be protected and taken care of when they serve our country.”

The Guillen family is also calling for an independent investigation of her killing, also advocating for an independent agency to be created to handle the military’s sexual assault and harassment reports.

Rep. Jackie Speier co-wrote a letter with Sen. Kirsten Gillibrand also calling for an investigation of the Army’s response to Guillen’s death. Lawmakers have introduced bills for decades in an attempt to reform the military’s reporting system, with little success.

“Army Secretary McCarthy personally met with LULAC members on July 10 and has directed an independent, comprehensive review of the command climate and culture at Fort Hood,” the Army said in a statement. “The Army is dedicated to enhancing prevention while emphasizing each member’s responsibility to intervene at the first sign of deviation from Army values.”

They said they provide “multiple avenues for the reporting of sexual misconduct, both within and outside the chain of command, to ensure every soldier has the ability to seek help and has a safe work environment.”

The Army urged soldiers facing misconduct to “call the DOD SAFE Helpline at 1-877-995-5247 while veterans can call Veterans Crisis Line at 1-800-273-8255.”

She will be laid to rest later this month. Her mother says she expects a military funeral.

“You go to war, and you fight with honor for your country. And if you die there, you die with honor,” Gloria Guillen said. “My daughter didn’t have to go to war because they killed my daughter here. They killed my daughter. She didn’t have to go to war.”

Gloria Guillen still doesn’t know the details of how her daughter was killed. Her husband says it’s too painful for her right now.

“It’s very, very difficult,” Rogelio Guillen said. “So much pain.”

“She will always be living on my heart. She’s always gonna be living by me,” Lupe Guillen said. “I admire her so much. I wanted to be like her. It just hurts me the most… She deserves to be here with me. Yet they took her away from me.”

Vanessa’s room, adorned with her marathon medals, is frozen in time. Her family clings to old photos of her smiling face. It’s an image of the woman whose story they hope can save the life of another soldier.

“If you know the abuser, report the name. Report the base where you are and to come out with me to seek justice,” Gloria Guillen said to anyone facing misconduct in the military. “All of you are still here… Not my daughter. My most precious being, they killed her.”

Now, she says she only gets to see Vanessa in her dreams.

“She’s strong. Ever since she was little — brave,” Gloria said in Spanish. “Where she is, she is very happy… She only wants one thing. She asks for one thing, nothing more. Justice, justice.”

Copyright © 2020, ABC Audio. All rights reserved.