My parents had an old car that I was able to drive for the first copule of years of my license. Then a P plater was showing off to his mates, did a burnout around a corner and landed straight in my drivers door (not fun), that was the end of that car.
I then bought my own, using largely money that my parents had been putting in to an investment fund since I was young. It was my fund, I could choose to use it for a car or not.
I would go with the putting in a percentage of the money option. I think it's good to help but definitely not good to pay for it all. And I wouldn't be fussed about it being a loan, I think a grant is appropriate, just not the whole value. As for her not having enough money for it - it will probably help her realise about the whole earning & saving thing to be forced to save enough money to keep the car running. Sounds like it'll be a stretch though, have you got enough room in the driveway for it to be parked there 90% of the time??
Maybe put parking signs up, $1/hr
PS. I haven't been in the situation the other way around - on the side of the parent, being only 27 and not having any kids
