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Compared to most, she's a good teacher.
Literal
She [topic-は] ordinary [with-と] compare-and good teacher is.
A trimmer phrasing of the same comparative idea: 一般と比べては uses the te-form of 比べる plus は, giving 'comparing with the average...' instead of the conditional ~れば form. The dropped の (compared to a phrasing like 一般の人と) leaves 一般 standing alone, slightly bookish. いい先生 swaps the literary よい for the colloquial いい. Note that this construction has a slightly unusual flavor — 比べてはいい先生だ as a fixed phrasing reads slightly oddly; the more standard alternative would be 一般と比べていい先生だ or 一般に比べていい先生だ.