I agree we are powerless to make them stop. However! You are not too powerless to have a conversation or two or twenty with her about what is going on.
Everyone needs a life! Alone, in the house all day, no car, no job, sounds very depressing! Does she have goals you can remind her of? Aspirations? It definitely sounds like this situation is going downhill and needs to change. So on an uplifting note while talking to her, are there things she would like to get involved in? Is there some reason she doesn't have a license to drive or want to get out of the house? Can you encourage her to join some group, take a class, get a job, or something?
If she's drinking because she is lonely, depressed, uninspired, etc., then can having something to look forward to in life during her daytime help her to change her outlook? I would think so.