If you decide to buy her a car, it should be understood that it's a one time deal, will not be replaced and she should not expect huge gifts next time.
Personally, I would not buy a 16 year old a car, period. But, I realize there are circumstances that require a 16 year old to have their own transportation.
My son turns 16 in two days. He will not be getting a car. Maybe, if he pays half ,. At 17, and has a job to pay for his own insurance.
In any case, if I were you I would buy a car that is very reliable and will not have a lot of repairs. I don't know about Cadillac, but a Toyota or Subura are the car I find has less repair needs.