If the feedback is indeed valid, then we need to know what it was. The criticism may be well founded and imposter syndrome is not applicable in that case.

Ideally they should be helping her improve or giving her actionable feedback. Obviously that doesn't happen in all case (not many really). She should work on fixing the issue, move to a setting/company better suited to her abilities, or find some other way to meet the standards set by the company/peers.