She sounds nuts. Gas and insurance are her costs, and no benefit to you. You're allowing her to put wear and tear on your vehicle which means the overall value is depreciating, you take public transportation which Im sure is a pain in the ass, and costs money, and since your name is on the title, if she injures anyone or causes bodily damage, legally you can be held liable for it alongside her. She can also total your car, and depending on how much you owe you may lose a lot of money.
I think you need to stop letting her use your car. No way in hell would I give someone a vehicle theyre ungrateful to use, and acting like she is some martyr for paying her own gas is ridiculous.