I agree - she needs to be off your list. You are not responsible for her. Period.
Ok - she has some emotional issues and you want to do the right thing.
Thats commendable. But really you are putting your self in a possition of liability. What if she is hitting more than plastic trash cans? If she is driving your car you may be held liable for damages. It certainly WILL hurt your insurance if she were to have an accident.
You said her intelligence is well below normal. Does she qualify as developmentally disabled? Your local bus service may offer door to door service. In my area its called access-a-ride. It picks up anyone with physical or developmental problems right at their door and takes them where they need to go. A schedule may be arranged or on call basis.
I have more ideas IF she is developmentaly disabled. I had an uncle and a cousin both with emotional / developmental disabilities. I would be happy to jot down some more resources for you.
"I have PMS and ESP. That makes me a *itch who knows everything!"
"Never EVER give up."