To me, it’s completely plausible that MM would have alcohol with her just because wherever she was driving. Like I said, I believe the girl needed significant professional help and was deeply troubled. Just sad her story had to end like it likely did.
I'll just respond to this particular part of your post right now. If there is any truth to this at all than that falls on Fred's shoulders for being an irresponsible parent. If she was as deeply troubled as you imply here than they should have taken her vehicles away from her and not allowed her to drive. But instead Fred was about ready to buy her a newer one that would make her want to drive even more. I don't care if she gets kicked out of a program. If she was that deeply troubled her family should have stepped in and taken her to a situation where she could be watched over more closely and not have access to things that could get her into trouble.
I personally think she was just a dumb and irresponsible kid but not a situation where she would need professional help or anything.