I advise you focus on being the parent and not the friend. You can certainly have a positive parent-child relationship but she needs a parent more than she needs a friend... especially in the coming years.
Personally, I give my kids a lot of space when it comes to school and their grades. If their overall grades are good, I see no reason to look over test scores, check homework, anything like that. They've earned their freedom and should be allowed to mess up now and them without having to both pay for it at school AND at home. If their overall grades drop, well, then we'd need to evaluate the problem together as a team. As of now, both the 6th and 10th grader keep their grades high. They do usually tell me if they've bombed a test or messed up an assignment. They are upset enough about it on their own. All I need to do is give them a hug, let them know that life will go on and offer help if they need it.
I wouldn't give her a hard time about this and I say this as the mother of one "intensely perfectionist" child and one "deathly afraid of failing" child. Your DD is obviously very worried about dissapointing you even though it sounds like she's a great kid with historically good grades. Perfectionism can be incredibly debilitating and raising a healthy child requires teaching them how to put their mistakes in perspective and learn from them. I'd start modeling positive ways to deal with imperfection... own your own mistakes, share your own less than stellar school moments, let her know that the learning process includes bad grades sometimes. Focus on the importance of learning instead of the importance of grades. Offer her help but be careful not to micro-manage (and I'm not accusing you of this.. I'm just saying it's something to avoid.)
