Aguilar was charged in July 2020 for her alleged role in Guillen's death. She was the girlfriend of the main suspect in the case, 20-year-old Aaron Robinson, an Army Specialist who was named a person of interest.
In March 2021, she asked a federal judge to toss her confession, saying it was taken illegally. On Wednesday, a judge disagreed, saying she provided the information voluntarily.
According to federal court documents, officers did not read Aguilar her Miranda rights at the start of an interrogation that took place on June 30, 2020. The documents state Aguilar was being questioned about Robinson.
You can read all 27 pages of the court records here.
ABC13's Steve Campion was the only Houston reporter at her court appearance in Waco. For the first time, video of Aguilar's conversation with investigators was revealed.
The 22-year-old is seen on camera saying, "I'm ready to get this **** over with" before sitting down to speak with them.
Aguilar's public defenders have not spoken publicly about the case. Eyewitness News also learned that Aguilar told investigators Robinson forced her to participate in the crime saying he held a gun to her head and demanded her to go to the Leon River that evening in April.
Aguilar also claims her phone was taken away and that officers did not tell her anything she said could be held against her in court.
READ ALSO: Gruesome details in report show how Vanessa Guillen may have been killed
Aguilar reportedly helped lead law enforcement to Robinson, before he was confronted and killed himself.
Meanwhile, dozens of people surrounded the court house in support of Vanessa's family.
"She knows how hard this is for me to be actually, like, sitting there, and it's going to get even harder," said Vanessa's sister, Mayra Guillen. "There's so many more things that ... they just told us that we're going to see, and whether we will want to sit there or not. I want to know everything. I want to know the truth. I want to know what happened, what they did to my sister. I feel like that's the fuel that keeps me going."
WATCH: Suspect in Vanessa Guillen case had 'no remorse' in court, attorney says
If convicted, Aguilar faces up to 20 years in prison with a maximum $250,000 fine.
"I just watched that demeanor, I watched those tapes and I just realized, you know what? We're dealing with a very bad person here and hopefully, she'll get the punishment she deserves," said Guillen's family attorney, Natalie Khawam.
COVERAGE ON VANESSA GUILLEN INVESTIGATION:
Why you may never see video of Vanessa Guillen's killer in his last moments
Army determines Vanessa Guillen's death was 'in the line of duty'
Army officials reveal new details in Vanessa Guillen case
Timeline offers look at tragedy and legacy of Ft. Hood soldier
New Vanessa Guillen mural created to fundraise money for family
For updates on this story, follow Steve Campion on Facebook, Twitter and Instagram.