Upon returning to the Woods facility, one caregiver brought two residents inside the building while Strauss dropped off another resident at another building.
Strauss then allegedly parked the van with 20-year-old Bryan Nevins in the back seat, locked the car and left to finish her shift.
It was 95 degrees that day and temperatures in the van reached 150 degrees. By the time employees realized Nevins was still in the sealed van, he had already died, according to investigators.
Nevins' father William told NBC Philadelphia Tuesday his son wouldn't have been able to get out of the van on his own.
"Brian was a very caring, loving, innocent child," he said in a phone interview. "Even though he was 21-years-old, he had the mental ability of about 2. He didn't have the wherewithal to open a car door and get out."
Strauss is charged with felony neglect of care of a dependent person, misdemeanor manslaughter and misdemeanor recklessly endangerment. The felony charge carries a maximum sentence of 20-years in prison, if she's convicted.
Police took Strauss into custody Tuesday afternoon and arraigned shortly after, authorities say. She's being held on $50,000 bail.
"We'll see what the life of a disabled child means to the people of Bucks County," William Nevins said.
An unnamed Woods employee was also suspended with Strauss just after Nevins death.