a ver frustrated mom, Please help!

My girl is a 10th grader. She gets most As and some Bs. But my problem is her attitute. She doesn't want to do any extra work even if she has a big test such as AP test on her way and she knows that there are still things she doesn't know the answer.

I have to admit I like her all As but if she has tried, I am perfectly fine with Bs. In my oppinion, a good attitute towards work and challenge is critical for a person's life, far more important than grades. However her attitute frustrates me the most. One after one, after many frustrations, I feel that I've done my best and I don't want to deal with it any more. She can be whoever she wants to be and I will have my piece. But I am afraid of one thing. I am afraid that someday in the future, I will regret and feel guity.

Any advice?

Thanks a lot!