If "she" is referring to her own mother, then it is incorrect. If "she" is referring to another person's mother, then it is correct (but only if that other person is male).

As I read it, there is a woman ("she") who looks exactly like this man's mother. So there are three people in the sentence (the woman, the mother, and the man: ie. the son, whose mother looks like this woman. Confused yet?). But as duguup points out, if the 'she' is the same person who has this mother (and no other brothers or sisters), then the phrase should read "...her mother".

It may be a tricky question, this sentence stand by itself without any reference. By definition, it is incorrect, to make this sentence correct, reference to "him" must be provided and connected.