I'm NOT new here, have been at this a number of years. So I can say with confidence
NO CAR. NO money for a car. There are rules and boundaries and actions, choices and consequences. Adult choices= adult consequences. I like what Lorelai said, it will be up to her whether she wants a car or alcohol more.
If she buys her own car, then you are limited as to what you can say about what she does with it, other than that its NEVER ok to drive while drunk as she could hurt other innocent people. If you finance her car,and/or if she is living in YOUR house, then you have every right to put conditions on it, especially where illegal drugs or alcohol are concerned.
Good luck. I've been in this position and it's not an easy one.
Hugs and love
Barb