I think the denial is fairly universal. Don't argue the point. If it seems to you to be an A, it likely is. I think there are many reasons for the denial: guilt, not wanting to define this "great" experience as something as negative as an A. I wouldn't talk to the OM, it's not about him, he's just an object of her feelings. Feelings that have a lot to do with you and your R, but a whole lot more to do with her. Communicating with the OP will fuel the fire, as they already know what they are doing is wrong and choose to do it anyway. It allows them to see you as the bad guy.
“No problem can be solved from the same level of consciousness that created it. ” – Albert Einstein