Honestly, I have no way of knowing right now without doing some snooping. I know who she is, but have no mutual friends and no regular contact. His behavior is what tells me that his fantasy life isn't as great as he thought it was going to be.
Anyway, I have learned that snooping makes me crazy. I had to stop in order to preserve my own sanity and to function as a mother. Also, when I do snoop, I think it comes acreoss in the way I talk to my H.
Ultimately, I decided that what she does or doesn't do is unimportant. I have to be true to myself, the person my H fell in love with and stayed in love with for 14 years. Not to toot my own horn, but I am solid, steady, a great mom, patient, and kind. She is a party girl with little self control or sense of responsability. Great for an affair, but not someone you want to keep for the rest of your life.
One more behavior that is positive, is that H has started telling me things he admires and appreciates about me. Not a ton, but it is a big deal to me because of how he had laid all of the blame on me when this started.