I'm sorry you're going through this, snoodledoo. I hope her friends stop enabling her. You just be calm and firm. Everyone takes his/her own path in life.
I have a panicking child. Her grades came in with a D in freshman seminar so now her life is over. Never mind the 2 A- and one A in her other classes (one of which is a 200 level class). I'm not happy with the grade, but as sick as she was the entire semester, I'm not going to freak out over it. Her overall GPA is higher than the one I graduated college with and I managed to go to law school. Deep breath, deep breath.....
I have a panicking child. Her grades came in with a D in freshman seminar so now her life is over. Never mind the 2 A- and one A in her other classes (one of which is a 200 level class). I'm not happy with the grade, but as sick as she was the entire semester, I'm not going to freak out over it. Her overall GPA is higher than the one I graduated college with and I managed to go to law school. Deep breath, deep breath.....
If that appears to be happening, it might be worthwhile talking to a family counselor of some sort, even if you have to go yourselves. Good luck. We're here with you! 

How are all the kids settling in after the winter break? DD is excited but says she already thinks this semester is going to be a lot harder than last semester. But she is happy to be back.