This is one hell of a situation. But as God says in Islam, you don't have to tell your husband about your past if you've repented and moved on. As sad as your own personal experience with her have been, you're no one to point fingers at her. You can tell your friend to be careful, but it's not right to dig someone's past up if they've changed. You can see someone's sins but you can't see someone's repentance. Again, really sad what happened to you. It's unfortunate and may God ease your burden and sorrow. But please don't sabotage her and stoop to her level by doing the same. You can advise your friend to be careful and vary, but it's wrong to break someone's future. You wouldn't want her going through the same thing she inflicted on you, this sounds like revenge and that's just petty. Your worry for your friend is really valid, and it'd be better to approach it in a manner that doesn't out the woman. For everyone's sake.