DB doesn't say to just ignore the fact she's in an A. You say you aren't permitted to reach out to her. To make things clear here, you can do anything you want. Nobody is stopping you. Least of all DB. It just won't work in your favor, that's all.
You say you feel you should be fighting for her. What does that picture look like to you. I am curious to know. Is it confronting her and,pressuring her to break off the A and be a faithful W to you? Is it trying to control what she does? Maybe just keep trying different approaches of begging, guilting, ultimatums, etc., until you stumble onto one that gets a better reaction? And don't forget a favorite one......confronting the OM and asking him to please leave your W alone.
So tell me, how would you handle it?
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!