My DD9 often expresses the same thing. She's a perfectionist who often pays too much attention to the negative in everything, and that means she turns it on herself as well. I can ask her to name one thing she likes about herself, and she won't answer. It's really sad, because she has so much going for her, and yet I can see at times where her lack of self-assurance becomes self-defeating.
Other times she's entirely self-confident, so it seems to be a mood thing.
Lately we've been working on her paying more attention to the good in other people, and we've seen a change in her behavior through that. Hopefully she can turn that change towards her introspection as well.
