My first instinct is to simply avoid contact with her in the future, although I totally understand the urge to write to her and straighten her out on a few things (like the fact that you never cheated on your H, that she can't get a green card, and that he has no money).
You are assuming, though, that she is a thoughtful and reasonable person, and the evidence so far does not support that.
On the other hand - it really does seem unreasonable to have your H in your home conversing with RT in front of you. It might be time to ask him to move out.
