。
She isn't the cheerful woman she used to be.
Literal
She [topic-は] before [of-の] like cheerful woman is-not.
以前のような ('the kind/sort she used to be') uses the simile suffix ような attached to 以前の ('of before'); the construction reads 'like the X she was before.' 快活な ('cheerful, lively') is a な-adjective on the more formal/literary side — everyday Japanese tends toward 明るい ('bright, cheerful'). The implicit contrast is poignant: she has changed, and the speaker remembers the earlier version. ではない closes with negation — gentle but unambiguous.