I think you keep telling her what you've told her, that she does qualify and that over time, she's going to feel more comfortable about how she fits into the class. My guess would be that this might be the first time she's had to stretch her learning "muscles" at school and it is intimidating. So I would share that concept with her, perhaps talk about times you experienced similar feelings and that it is normal.
As to grades, families have different philosophies about them. Based on your post, I'm guessing yours isn't overly concerned about all A or A+ marks (I'm not, either, for better or worse). If that's the case, think about how to explain grades as simply a way of tracking progress over time, identifying areas that one has mastered and ones that still need work. Above all, make sure she feels that they are not a reflection on her worth and that she knows the other kids are being, for lack of a better word, tacky.
