I have twin girls. When I get my girls dressed, one of them in particular has, on occassion, said things like, "This looks stupid. No one will like me." I've never ever told my daughter she looks stupid or that people won't like her, so I don't know where she got it from. It breaks my heart every time. Also, when she's angry about not getting to watch a movie or I try to lay them both down for a nap, I get, "You don't love me." I'm so worried these days with the media giving off messages to young girls that they always have to be skinny or have the most recent fashion.
It's always upsetting to hear these kinds of things from a child, especially a young one. Extremely verbal little girls are particularly known for this kind of commentary. Don't panic yet -- children this age often try these types of statements "on for size" to see how others respond; they're practicing their verbal and social skills. They don't have the maturity to fully understand what they're saying yet.
It's important to take these comments with a big grain of salt. She's looking for a reaction, and giving it to her will only increase the chances she'll keep it up. Next time, look at it as an opportunity to help her say what you think she really means instead. When she says, "This looks stupid. No one will like me," tell her it sounds like she's worried about making (or keeping) friends. Ask about her friendsn and what she's heard other children say about clothes. Help her think through the complicated ins-and-outs of her preschool social life and role-play challenging situations she encounters. When she says, "You don't love me," try responding: "It sounds like you're mad at me because I'm not turning on a movie. I can understand you're mad." Don't address the surface statement -- which she doesn't fully understand, anyway -- instead, address the real feelings underneath. That way, you'll help your verbal little girl communicate her feelings more clearly as she grows.
If this doesn't help, please consult a child therapist who can help you decide if your daughter's negative self-talk would benefit from some professional support and guidance. It's always a good idea to have a trusted expert on hand in cases like these.