You are right to not take it any further until she has left her husband. It will be difficult for her, as not only her own feelings of guilt, sadness, failure etc but the feelings of her family and other close friends around her who may not approve of her leaving her husband.
Help her leave him, if she really wants to, but take it from someone who knows, starting relationships with people who are not single in the first place puts you in a very vulnerable position until they are sure that making that break was the right thing for them to do.