The first thing to do is not to let yourself get too upset. Dominance patterns can change quickly with young children, and the little girl who is today’s tyrant may be looking for companions next week. This one definitely will if she is as bossy with all the other children as she is with your daughter.
But a more important thing is to talk to your daughter’s teacher. Try to describe the situation without putting the other little girl down too much. If this is a chronic pattern in her class, the teacher will have noticed. Urge her to find ways to make certain your daughter gets her share of favorable attention—for instance, being invited to bring special things for “Show and Tell,” planning some activities she knows your daughter will enjoy even if not in the “clique.” Also I would try to help her make friends with one or two other children in the class (have them over, take them to special places, etc.) to increase the likelihood she will have someone to play and work with and not be bothered by lack of attention from the “star.” And be sure to compliment the work she brings home.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.