In a way, she is. Just as 2-year-olds straddle babyhood and childhood, tweens are perched between childhood and adolescence. As both toddlers and tweens transition to the next stage, they try to act more independent. Two-year-olds do it by responding "No!" to every request you make; tweens do it by opposing your suggestions and criticizing your opinions, says Debbie Glasser, Ph.D., a clinical psychologist in Richmond, VA.
Get her to open up. When your child says, "I hate this," ask her, "What don't you like about it?" This will get her to express herself more constructively, and show that you care about what she thinks.
Suggest that she call a friend or favorite aunt when she gets on your nerves. Since there's no need for your daughter to disagree with everything this other person says, she may be able to talk about whatever's really bugging her (it probably isn't what she's complaining about).
Hear her out. Maybe that dress is too babyish, or mushrooms do make her gag. Let her weigh in on more decisions and she may be less likely to moan about the ones you make.