Your sentence b is correct. You wish (now) that you had met her (in the past). You need "had" because "wish" takes a past tense (eg "I wish I was rich"), and so the hypothetical meeting needs to be doubly in the past. This means your sentence a is wrong. As already answered, sentence c implies it is still possible to meet her.

You could also use "I wish I could have met her."

Your sentence b is correct. You wish (now) that you had met her (in the past). You need "had" because "wish" takes a past tense (eg "I wish I was rich"), and so the hypothetical meeting needs to be doubly in the past. This means your sentence a is wrong. As already answered, sentence c usually assumes it is still possible to meet her.

You could also use "I wish I could have met her."