DS7 does this in his foreign language class. I think it's because he doesn't want to be wrong. His teacher and I have told him that it's okay to be wrong--that's how he'll learn what's right! But he often mumbles out answers.

Given the foreign-language component of school for your DD, I'm thinking she might be doing the same sort of thing. FWIW...

So I guess I suspect a lack of confidence: not "normal" exactly, but not a reason to panic either. Maybe just something to talk about.

Kriston