The 39-year-old's body was recovered inside her vehicle, which was found in the parking lot for Huebner Oka Center in San Antonio.
Per the guard, the car had been there "for about a week" and, according to the San Antonio Police Department, there were no apparent signs of trauma.
Powell's mother also confirmed her daughter's death on Facebook, writing, "My beautiful daughter, Christina Powell, has been found, deceased.
She was already running behind schedule when she left and reportedly phoned her office to say she would be late.
Instead of finding Powell, they spoke with her eldest child, who said his mother should be at the office.
"We didn't really have any kind of in-depth conversation. It was basically, 'Good morning.
She told me she was late," Powell's mother -- who lived with her daughter -- recalled of their last moments together that morning.
Per the police flyer about her disappearance, Powell was described as being "diagnosed with medical conditions that require a doctors (sic) care.