Board Thread:Legitimate Canon Questions/@comment-27945504-20160309204117/@comment-4091815-20160309204450

It was a way to bring Crystal back to the show which is something they wanted to do.

She didn't actually look exactly like Allison. She was two years older, had different hair and they used makeup to slightly alter the shape of her face. The resemblance was striking but hardly unusual based on genetics. It also made the Sebastien's hesitation at exactly the right moment make more sense and gave the Allison fans all sorts of feels because she is still saving people.