ladybug23,
Has something changed in your daughter's life? Friends moving or friendships ending or changing? Can she drop a class and take it in the Summer - this might take some stress off now. At 17, kids are going through a lot of changes and school work can suffer. Does she have an outlet - yoga, running, or swimming to relieve some stress? Sometimes we are so used to what is going on in our lives, we don't even notice the stress. Meditation can also help. It does help me get through problems and reduce the stress, and maybe it will work for her.
Do you have dinner together as a family? This is really simple, but it gives you time to talk and share and really does help to find out what is going on and to give everyone some much needed "down time."
Take care,
lady moon