。
She admitted that she was in the wrong.
Literal
She [topic-は] herself [subject-が] is-being-mistaken fact [object-を] acknowledged.
誤る (あやまる) means 'to err, to be mistaken' — a more formal, written register than the everyday 間違える. (Confusingly, 謝る — same reading あやまる — means 'to apologize'; context distinguishes them.) The progressive 誤っている describes a state of being in error, not the act of erring once. 認める ('acknowledge, accept') paired with こと-nominalization is the standard frame for admitting a fact about oneself or the world.