I work at Fred Hutchinson (although I don't know Cheryl), and while we are allowed to park at work if we travel solo, we have to pay $125 for a monthly parking pass. A carpool parking pass is 1/4 of the cost of a single traveler parking pass. There are a number of other incentives to encourage us to carpool or take public transportation. So... a lot of people who work here carpool or take the bus. If she didn't have a parking pass for a single car (which she most likely didn't if she belonged to a carpool), parking would have been a real challenge. Patients are seen at the main campus where Cheryl worked, and they will often opt to avoid paying for parking in the garage for patients, so it's really tough to find a parking spot on the street.
Something else I want to chime in with: It has really resonated with me and my coworkers in my department that she turned back to get her badge. We really need our badges here: to enter buildings, to get through doorways, even to use equipment like the copier machines. In my department, we need to have our badge with us to use the bathroom. It's miserable to have to borrow someone's badge every time you need to get through a doorway or use a machine. I completely understand why she would take the time to return home for her badge.