My thing that helped me in sictuations was
"I use to care,but i have a pill for that now!"
All kidding a side,if she is not willing to come to terms with the reality of life or in lame terms get her crap together,then unfortuanly reality is going to come hard for her.
She sounds to me to be a young know it all who takes alot of things for granted.
And unfortuanly she is going to learn very hard lessons in life.
I feel for you and wish we could all wave a magic wand and "poof" the problem solved,but this is something that you are going to have to do on your own.
The most advice i could give you is called "Tough Love" let her know youll be there for her when she needs you,but also let her know that you mean business and will not put up with her antics in the same sence.
If not,then you have to do what you have to do and let her make her own bad choices are on her own.
The most you can do is give her good advice,the rest is up to her.