She also says adults don't listen to children, just because they're children (I agree, that happens). When she's with other kids, she usually prefers to be by herself. I've told her that she needs to take the other kids' feelings into consideration, otherwise she'll lose all her friends. She is in Girl Scouts and Score! I would like to get her into sports, to learn sportsmanship and channel some of her aggression, but she doesn't want that.
She doesn't have a problem with kids liking her -- adults just steer clear -- but the kids are not going to keep putting up with this behavior. What else should I say to her to help her understand this?
Sometimes gifted children use intolerance to mask other kinds of feelings such as insecurity, loneliness, or low self-esteem. They express disdain because these other emotions can be too frightening or overwhelming to acknowledge. My first suggestion is to see if you can help her determine what she really is feeling and find better ways of handling the situation. The book How to Talk So Kids Will Listen & Listen So Kids Will Talk by Faber and Mazlish has some excellent strategies for beginning this kind of conversation. Perhaps she's finding it difficult to connect with her chronological peers. If that's the case, you might help her locate some interest-based activities where she can make friendships with kids who have a lot in common. If she has that point of contact as the basis for a friendship, she's less likely to be critical.
From your daughter's comment about not feeling heard by adults, it also strikes me that she might be assuming that her opinions and feelings don't matter. Acknowledging -- as you already have -- that this sometimes is a problem, is a good first step. Also important, however, is letting her know that you empathize with her feelings about this and that not being heard feels awful. Then you might problem-solve with her about alternative ways to make sure that she is heard so she has other ways to respond, besides intolerance. Good luck!