A. No, says Tina Tessina, Ph.D., a psychotherapist in Long Beach, CA, and the author of It Ends With You: Grow Up and Out of Dysfunction. Your daughter's sudden preference for girls is developmentally normal, and her anti-boy proclamations are just her way of saying, "They're not like me."
Though most toddlers can tell whether someone is a boy or a girl, it's not until they're about age 4, when they're starting to form an identity of their own, that kids start noticing differences that set the genders apart -- for instance, that most girls like combing dolls' hair, while boys tend to play rough. It's also when they start forming their own opinions about what they don't like -- from broccoli to, in your child's case, boys. She's simply gravitating to the kids who are doing what she enjoys, and away from those who aren't.
This isn't to say your little girl won't ever play with boys again; gender's just one of the factors children consider when making friends. A shared interest in bugs or a similar outgoing temperament can bring two 4-year-olds together -- no matter their sex.