Sounds like she is engaging in a lot of self-criticism.
If she has a social network of supportive friends in her current classes then having to start all over might be further destabilizing, if she is verging on actual depression. Is she enjoying her usual fun activities? Wanting to go do things with her friends? Her usual self in other ways? Is her negativity limited to academic type subjects or is she feeling negative about a lot of aspects of life?
The parent teacher conference sounds like a great start. If that doesn't seem to shed light on it then perhaps a visit with a counselor, psychologist etc who may have experience with girls in puberty, get some sense of how seriously to take her comments, etc.
Polly
