advice needed

I really need advice.

I think my ex is taking advantage of me because I have a car, and she often will ask for a ride, only to add 2 or 3 extra stops, or want to spend much more time somewhere than she mentioned before she got into the car.

I put up with a lot because she is the sole caregiver of my disabled daughter, but then today she spent part of the trip insulting both me and my mother and claiming we were going to hell.

I really want to set a boundary here, but I don't know how to without it hurting my daughter.

advice please.