Susan,
Keep in mind that Kasey has learned a lot and she doesn't want her old life back. I think you have to trust that she make the decision to right her wrong. She didn't ask to come home......give her a chance to figure it out.
She may know the dates more than you think. Sometimes we don't give them credit because they are addicts. She may be thinking of her past with him also. Sometimes they dig up old dirt in their minds and it hurts. This doesn't mean she will go back to all of her old ways. She had a slip and she realizes it. She is paying the consequenses of it. She is not responsible for her friends relapse. Her friend is responsible for that. No one can make you do what you don't want to do. How do you know it wasn't her friend who encouraged her. In any event they are both at fault and responsible for their own behaviors.
I am glad that you called her back to tell her you loved her. Letting her know that making a mistake isn't going to take away from the relationship that you are rebuilding. Give her a chance.
I'm keeping you and Kasey in prayer and sending mom hugs.............Lo