Kids know when they are different from others and when they struggle with things that others get without a problem. They get more negative feedback at school and from peers than other kids as well. This is why ADHD is often accompanied by anxiety, depression and/or defiance.
Look at the marble system by ogram (top thread of this board) for a positive reinforcement system. The more positive feedback and rewards for the good things a child does, the more their self esteem grows. Coaching her on social skills (even on things you think she should know) would be helpful as well. ADHD kids are about 30% behind thier peers in these areas, so don't be supprised if you have to coach her as though she were 7 sometimes.
The meds have helped my daughter become successful at school and more accepted by her peers, furthering that self esteem.
ADHD children always get fusturated or disappointed in themselves then "normal" children (i hate the word normal but i used it) and their self esteem is not as high, I think it is important to always praise them when doing a great job!! our children are very blessed to have parents that support them and work with them as much as the parents on this board do, but they are not aware of anythign other then what they feel and it is hard to change that feeling unless we focus on the good and go above adn beyond praise :-)