I think now that your daughter is starting to ask questions about her issues, it would be best not to wait any longer to tell her the diagnosis. I think that by giving her a reason why she has difficulties with certain behaviors will help her feel a little more self-confident. If she does not know what reason she has trouble with these things, she may feel like she is "wierd" or "stupid". Yes, I understand that some children feel "different" when told they have AS, however, if she is starting to realize that her behavior is different then the other kids and cannot figure out why, she is more likely to blame herself and get depressed. By giving her the name of her condition, it helps her understand WHY things are different for her, and she will feel more comfortable asking her family questions about the different issues that are bothering her. Also, you can see if she would be interested in taking social classes that specifically deal with AS and children with social troubles, and helping her learn and understand more about the people around her.
My nephew is 8 years old, and while his parents haven't directly told him he has AS, he has been told that he understands things a little differently than many other people do. Since he has come to this realization, I have noticed an increased confidence in him asking questions about appropriate social behavior and other similar issues. He now feels like "ok, so I don't quite understand something, but I can find out how do deal with it" as opposed to feeling that he was just strange for not understanding things that other people took for granted. It has also allowed us to gently correct him if we see him doing a behavior that is not considered socially correct, or appear "weird" without him getting mad at us and feeling like we are picking on him. For example, he headbangs alot for comfort, and we have been able to tell him that we understand his headbanging and that it comforts him, but that if he did that behavior around school or other kids, the children might find it unusual. This has helped him immensely, and has helped to make him aware of some of the things he does, so that he does not get picked on in school for them. (He always feels like people are laughing at him, and he gets embarrassed easily, so he's happy if we correct him on this, so that the other kids won't laugh at him. He knows he can continue his "stims" whenever he is not in public, and no one will bother him or laugh at him.
I know there have been numerous discussions about weather or not to tell your child he/she has AS. But I believe that however long a parent chooses to wait, once the child starts to realize that things seem "different" to them, or questioning why other people find their behavior odd, that parents should not wait any longer to tell their children the truth.