Grounding her is not very logical at this point unless you know that her behavior is absolute defiance. I would urge a meeting with you and your daughter and her teachers. Talk about what they perceive as the problem. It is probably very different from what she sees. Ask about her abilities and strengths. Work together, make a plan including suggestions from her. Follow through with the plan. If it doesn't work, talk again.
Another suggestion might be to ask the school counselor to meet with your daughter for a few sessions to see if the counselor can determine the source of the problem. It may not be the work at all, but your daughter's social interactions. Kids this age can be very rough on one another, and she may feel that she doesn't fit in. Her counselor may come up with ways to help her feel more comfortable both socially and personally.
Most importantly, listen when she speaks. Hear what she says between the lines and follow up accordingly. Continue to support her with expectations and boundaries.