I agree re: the unicorn. And while Siz hasn't done either of those things, she also cares for him. Even after what happened to Justin, I don't see Siz getting shouty and calling him a bastard as Sally-Anne did. She openly says she'll miss him- and while she might not be happy about that, it's still there.

I don't see her hurting anyone to help him, but I think she is still attached enough that he could probably manipulate her if he wanted to.