You say the problems occur in her already establish groups. In my view girls can be quite ****** at this age. The comments are probably mostly made out of jealousy in your daughter being so confident but also because it sounds like she's probably always trying to be the leader of the pack. I remember girls at school who always wanted the first say and want everybody else to do what they wanted and it grew tiresome to the point they would be alienated. I would advise your daughter that she needs to start listening more to others and take a back seat. If others don't like her ideas then she should ask them their ideas and go along with them. If she wants to fit in she needs to be asking other what they would like to do instead of her initating all the time.
Don't let her become one of those self obsessed people that you find in many work environments who never listen to anyone else and will talk over others to have their say.
If your daughter's bright she will eventually learn this for herself and she will need to accept that she can't be liked by everyone and not to worry about her popularity. It's better to have a few quality friends than lots of accquaintances. If she has some good mates then she could be brave and ask them why some kids are off with her.
Don't worry for her, just be her support and keep her confidence up.

Thank you for your reply. I have tried to bring up the subject of her perhaps being a bit pushy but she insists that this isn't the case and i don't wish her to feel that i am not being supportive and lower her self esteem even further.

I am going through a similar problem with my 7 year old daughter. Another parent who I WAS friendly with told me that my daughter was bossing all the other girls around during class time and play time. I got a diffrent story from my daughter so I contacted the school to ask their opinion on the matter. They told me that whilst there have been a few incidents at play time (not just my daughter) nothing during class time it has been dealt with and they are not worried and neither should I be. However, this parent still insists that it is carrying on, this parent hasn't contacted the school or discussed it with them and refuses to accept what the school have told me. Its worrying me and (rightly or wrongly) I have told my daughter to keep her distance from this girl/s in question. I think as parents we take personally the knocks our children take in life.I know how you are feeling, its the worst feeling ever because they are at the age where THEY have to deal with it under our guidance but ultimately they have to go to school and face this situation not us. I think it helps to get a bigger picture sometimes, maybe contact the school and see how they view the situation as they must come accross this all the time, if your daughter had never had any friends at all at any time then I'd be worried,just remeber yor daughter is not the only one to go through this.Good luck.