Well, you definitely want to celebrate her success, but my biggest advice would be to focus on her efforts and not the results. You know, really encourage the effort and discipline that went into those grades, so you're encouraging the behavior as opposed to solely recognizing what she achieved. It's kind of like how you want to focus praise on character more than something beyond your child's control such as good looks (or intelligence in your daughter's case). So just make sure the emphasis is on what really matters and what really is within her control--her hard work. You just want to be careful to make sure that she realizes that you'll be proud of her if she tries her hardest, no matter what the results are. This is coming from a person who never earned anything but As my whole life, including college. My parents never put any pressure on me, but were sure to admire and recognize my discipline. And while they also admired my natural smarts, they made sure to place the emphasis on something that was within my control and a reflection of my character.
Also, I would make sure to emphasize how maintaining this type of effort and the resulting grades will help her in the real world, because when it comes down to it she is the one who benefits from this, so draw that correlation. Doing well in school will effect her future very positively, and that's the true reward. So encourage and praise the heck out of the wonderful little girl she is.