2001 Chrysler Sebring engine starts then immediately shuts off

A couple of months ago my daughter’s Sebring engine began shutting off immediately after starting. We brought the car to my usually reliable mechanic. They couldn’t find anything wrong. The problem became more frequent (every 2 to 3 starts) and we brought it back to my mechanic who determined it was the car’s computer system. $1700 later the car is ready to be picked up, my daughter gets it after the shop is closed, and it wouldn’t start! She left it there, got a ride, and, one week later the Sebring is still at the mechanic’s. They told us it starts every time for them and they don’t see any problem. After researching on the Internet I thought it might have something to do with the immobilizer but they told me that tested fine. I’m at a loss over what to do.

It was after hours, so did she use the same key the shop used? If she used a spare key, it may not be synced with the immobilizer, since they did computer work. She needs to go get it when the shop is open to work this out.

Was she ever able to use her key again? Or was there another problem in the system?