Gutwrenching-
It is an addiction. I know exactly how you feel. I watched my husband cry that he had messed up his whole life. I kept it all a secret for him b/c he was so worried about his job. Then a couple of smoke signals sent out by ow and he is back at it. I don't have any other advice than I know how you feel. I will say this though, the fact that she came to you and told you about it is promising. Some of the sites that I have been on have said that it is very likely that they will get in touch with their affair partner, but she told you about it instead of resorting back to the lies. I really think that the lies make it the worst. So i think that you are doing the right thing giving her a few days, continuing to db and trying to leave the emotion out of it, thank her for being honest with you. Whatever you can do to keep her talking and being open with you will be helpful. Maybe do this for two or three weeks before going to plan b. I don't know if this is a good idea, but one book that I read " My Affair Became the Best Thing That Ever Happened to Me" her circumstance was somewhat similar. Her husband ended up leaving for two weeks, but when he decided to move home he contacted the affair partner, as friends, for a couple of weeks. She talks about how she just tried to listen to what he told her. Then a few weeks in she gave him a letter that outlined exactly how she felt, and what she wanted in the marriage. I believe that she got the basic format for the letter from James Dobson's book "Love Must Be Tough".
I know I am rambling, and I don't really know first hand b/c my husband just keeps lying to me about his contact. But I would think that the fact that she is talking to you is a good sign. This woman says in her book that it is darkest before the dawn.