I went back and re-read the OP and some of you should, too. The wife's issue isn't that she was betrayed for so many years, but that her husband crossdresses.
She assumed he was gay, wanted to be woman, and is a sexual deviant, a sickness that needs curing. Sure, there were many years of living a secret life, but assuming that the lie is the main problem is reading into the OP something that wasn't there. I think the wife is one of those who cannot tolerate a crossdressing husband. Most of her assumptions about crossdressing are incorrect, but that's her reality, and Samantha's.
What good is it doing to remind Samantha that the wife should have been told long ago? Samantha is seeking advise on where to go from here. This forum is full of testimonies of cd's who thought that marriage would cure them. OK, we were all wrong. We don't get a do-over. Must go forward.
I prefer "counselor" to "therapist". Therapy suggests that there is something wrong with you and a therapist can fix it. Counseling suggests working on a relationship between people who don't see eye to eye and need help getting there. Just my perception.
Whatever you call it, why would a couple go to counseling or therapy? My guess is that she wants him cured, and he wants her acceptance. Without a common goal to work towards, how can it succeed? If you don't know where you're going, how are you going to get there?