Be direct, but prepared. Be prepared for tears or screaming. Have a bus schedule in hand, suggest she carpool with employees at her business, tell her you'll help her pick out a car this weekend.
If she says that you've always helped her & why can't you continue, tell her you are helping her, you are helping her to be independent. If you need some white lies, tell her you have to work late, or you're taking a class after work or you need to run personal errands after work. Tell her for the sake of your mental health, you need to sleep in on Sundays or exercise or go to church.
Do not help her financially unless you don't care if you get paid back. Do not let her borrow your car again - use that insurance excuse. Please don't let her continue to use you - she's gone way over the limit. I speak from experience, that this will end up hurting you more if it continues than it will hurt her now to break it off.
WIP: GAAA for m&d, purse for grandma (needs assembly), Grannie Smith Cardi (still), 3 quilts, maybe five
In the Wings: felted clogs, socks
Recent FO: dishcloth for swap, booties for cousins babe
KALs: Grannie Smith, Monthly Dishcloths, Mason-Dixon