Technically, the sentence does not break any grammatical rules. Semantically, it is poorly written. The central noun in the appositive phrase is change. So we look in the adjacent clause for a noun phrase that can the appositive can refer to. Our choices are woman and she. Neither of these can be described as a change.
I suppose you could change the appositive into a subordinate clause, but there is a simpler solution:
In a drastic change from her old style, the woman now dressed very differently than she used to.
Grammatically, this is now quite different. The modifier is a prepositional phrase rather than a noun phrase. It functions as an adverb and describes the manner in which the woman dresses.
I don't think the original author intended to write the sentence this way. Some people just struggle with appositives.