A teenage girl is in custody on suspicion of murder after a San Diego-area Uber driver was stabbed to death in her vehicle last week.

Around 3 p.m. Tuesday, a 911 caller said they had witnessed a woman being attacked inside her vehicle in National City, Calif., KSWB reports. When police arrived at the scene, they found the woman unresponsive.

The victim has since been identified by Uber as 58-year-old Raquel Spohn Wehber, an Uber employee based in the San Diego–Tijuana region.

While a motive for the alleged attack is not yet known, witness accounts led investigators to the arrest of a 17-year-old Uber passenger seen fleeing from the crime scene, KSWB, KNSD and WBTS report.

The suspect’s identity remains confidential due to her age, but an arraignment held virtually in juvenile court Friday indicates she is being charged with two felony counts — one for murder and one for torture,  the San Diego County District Attorney’s Office tells PEOPLE. She has pleaded not guilty to the charges.

As authorities continue to search for a possible relationship between Spohn Wehber and the suspect, the victim’s loved ones are mourning their loss.

“Raquel was the glue of our family,” one of Spohn Wehber’s daughters, Daniela, wrote in a GoFundMe campaign established to get her family back on their feet. “She was filled with laughter, lived life by her own terms and always managed to make friends wherever she went. She lived life with joy and loved the time spent with her family. She will be forever missed.”

According to the fundraiser, Spohn Wehber leaves behind two daughters and two young grandsons.

“While my sister and I are appreciative of all the memories shared with my Mom, my nephews will never get to experience the greatness of my Mom,” Daniela wrote. “They were robbed of that opportunity when my Mom was murdered.”

Uber issued a statement to PEOPLE, saying, “The senseless and brutal crime that took the life of Raquel Spohn Wehber is heartbreaking and our thoughts are with her family. We stand ready to work with law enforcement on their investigation.”

KSWB reports that as of Thursday, the National City Police Department was in the process of obtaining a search warrant for the Uber account used during the attack.