Oh my. I'm leaning towards giving her some information. There relationship is so precarious because he is dangerous and out of control. I think small amounts of information starting now will better prepare her for the reality of her relationship with him in the long run. She isn't going to go spend the weekend with him. As she grows her expectations of a father will change (and at this point he isn't going to meet them) and giving her some information now will hopefully help her understand that this is about him, not her.
My experience is that my kids thought their dad hung the moon and he vanished into alcohol and then vanished for real and they were not prepared for that. Not that a child ever can be but it all happened quite fast for them and that was hard as they see/saw it as a problem with me and then themselves -- not with him. I am trying very hard to make sure they know this is not about them.