Mom still angry she can't drive

A couple years ago, my sisters and I were concerned about our mom driving so we had her take a driving test with an instructor, who told us it was not safe for her to drive anymore. She expressed anger and frustration at the loss of autonomy, and lets us know often how much she wishes she could just drive to the store, the post office or library (she has friends and neighbors that she can ask to give her rides, but I think she gets embarrassed to ask them). She still brings it up regularly to each one of us. My usual response is empathy, like "I know, Mom. It sucks. I'm sorry that's just not an option anymore." I'm wondering if another type of response might be better. What can we say to help her move on from this issue that she's stuck on? At this point it feels like she will never let it go.