Tangent

 

Does she eat a full breakfast?  Does she have her own room, with all the furniture fit for a teen?  Does she decorate her room?  Do you pay attention to her clothing?  Do you ask her every week what she needs (not necessarily school-related)?

Stop making (implied) demand (you'd better get an A on this test.)  Start think through all aspects of her life and pay attention to details.

Remind her that she is doing these things for herself, not for the parents.  There is a wonderful world out there waiting for her, but she has to get ready by making an effort.  Life is a beautiful thing.  Think of ways you can help her realize such.