Retracting My Helping Hand

Family-
There are those family members you can't get enough of. Then there are those whom make you want a DNA test from to prove relation. I love my aunt. She's good entertainment. Before the moments together end, I know she's going to crack me up. Then there is today. I go out of my way to drive 20 minutes out to pick her up and take her to work an hour away 2 days in a row because her car is busted and she has no means of fixing it. Monday I let her borrow my car altogether. Thursday too. She complained about getting gas at $20 a pop twice in a week!
There was no consideration of the mileage she is accumulating on my car and the fact that I have to travel by foot or public transportation without my car that was never meant to get her from destination to destination but me instead. She didn't even recall that I had just put gas in my car before I let her borrow it Monday. I have errands to run but still she complains.
We are double tripping twice a day for her connivance not mine. She isn't insured on my car. Why is she complaining about gas she would have ultimately put in her own car provided it was up and running. The nerve of some people. I will not be taken advantage of. She has today to cool off but my birthday is Friday the 21st. She better not complain again. I don't travel more than 3 miles from my home to run errands so it is she who is burning the gas. I don't understand her frustration.
What do you do when your help is unappreciated? A big part of me wants to lay her out. The respectable part of me will just keep quiet. She is still my aunt which is an authoritative figure. I shouldn't argue with her. She probably won't apologize. I will have to retract my helping hand because she thinks its owed. Its not. I don't have to help her. Trouble is, how do I do that without the argument after?
What happened to adults having manners and just saying thanks. You have to pay for a cab; why not pay for gas when borrowing some one's car?