We've had near similar situations while our girls were beginning to drive. Separately, because they are 4 years apart, I went over the car they were about to be driving all the time. I'm far from being a gear head but I do know that it takes much more than just putting gas in a car to get it to go and I knew these girls needed to have that hammered home before having the responsibility of having a car full time.
I kept reiterating; "if it breaks down because of your neglect, I won't fix it immediately and you WON'T be using my or your mother's car to replace it." Downside was that they hounded me for every squeak, rattle and idiot light that went on. The cars still needed repair from time to time but they knew how to check the oil and trans fluid. Thankfully, no major issues while they were driving and living at home.
The oldest went out and bought a car on her own with her boyfriend, despite our advice not to, while she was in college. The car ended up being a lemon and she looked to us for help. We told her that we gave her help by advising not to do it but she did it anyway, now it was her responsibility to make it right. She went to court against the dealership and won her case. They took the car back and gave her back her money. Lesson learned and a life experience that she's used to this day.
The youngest one... not so much of a good story but situation was more fender benders that she tried to fix on the down low without asking for advise or help. Kinda messed up Di's credit score on the car she co-signed for. Thankfully, she wised up and made a full recovery! ;DDD