。
She was worried about being criticized for her performance.
Literal
She [topic-は] her own performance [subject-が] be-criticized [thing-こと] [object-を] was-apprehensive.
自分の演技が批判されること ('the matter of her performance being criticized') uses the passive 批判される ('be criticized') inside a clause, then nominalizes the whole thing with こと. That noun phrase becomes the object of 懸念する ('to be concerned about, to apprehend'). 懸念する is a formal/written verb for anxious anticipation — fitting the inner texture of pre-performance nerves.