Sick indeed, but if a child things it's alright, it will do it.
I would advise sitting down with the parent and talking things through.If the mother was so helpful it could have been the father doing it behinde her back.But as Noirkitten said, it's possible that she didn't learn it from a parent at all. It could be a siblings, cousin, any older relative, some other child or what not.If the girl things this is alright, something is obviously not well with the way people acter towards or around her.