God ... your story feels familiar. So, here is ours. I hope it helps.

I have known the same T for years. And I only just recently drew the line and forced a conversation about it. But she had pissed me right the F off. I say I because I am the one who actually confronted her, and finally told her how much it bothered all of us that we could not talk about it - admittedly at a raised volume. I was pissed, and she was frustrated - I could feel it coming off her in waves - but I am glad I did. She listened, and then *ping* - I saw a light bulb.
I think she finally put the pieces together, it might have explained something that was driving her to frustration (she is normally very ... calm, unemotional ... stoic).

And That is how it got buried:
We told her about US and the confirmed dx, when I started seeing her over 5 years ago. But we were in really bad shape at the time. Really bad. Pretty much, I remember questioning my sanity. Feeling everything that defines crisis: couldn't work, couldn't eat, couldn't sleep, cutting, burning, actively wanting to die ... HELL on Earth. That kind of bad. There is also a recollection of her saying that she did not think much of it and "there is only one body, so I just want to talk to one person". So, it was not talked about. During the confrontation, she stated that if I had it before, don't have it now. I wanted to punch her in that minute. How could she know if she was not even looking? So I yelled, and then the others started talking, and then this dawning look. I could see the "OMG what did I do" look on her face. She had opened her opened diagnostic eyes and suddenly I guess we made sense. And well ... I left feeling a little lighter.
The others ... not so much. They think that she is going to bail. Others therapists who claimed the ability and the skill set have before. And it has caused damage.

You might wonder: how could she not see it? Well, we tend to switch/trade out rapidly when in her office. So, though she knew that we had been diagnosed, we just never told her who was or was not there. We thought she saw us, but that she just did not care about the dx, and I think she assumed that the woman before her had made it. And because of that woman's actions (I refuse to call her a therapist) - my T could not trust it.
But she made the mistake of assuming and she was wrong. Her job though, was to help us get to a point of stability so we did not die, and she did.
Then quit treatment, and did not see her for a couple of years. Went out, got a job, then a better one ... then got a real career doing something that pays well, and provides ... high functioning to say the least. But still broken in ways that I think you can understand.

So, when we returned, she continued under the assumption that it was just severe PTSD and not also DID.

But the thing was and is - rather we like it or not - the original diagnosis of D.I.D. was confirmed. It was made by two different "experts" in the field, and two different hospitals that had dedicated clinics back in the '90s - way before we ever met the woman who she had assumed made it. The dx was real. Didn't mean we embraced it, or like it, or felt anything positive about it. It just was.

So, when things started kicking off again we went back. Some things - no matter how buried - will eat your lunch if not dealt with. And we are masters at avoidance. That is at the heart of D.I.D. We switch to avoid something for which we can not cope. It allows us to forget and displace ownership of our own history. It does not go away just for want of it not being real. And it takes guts and strength.
I hope we are strong enough now. Hopefully she does not bail. She [/I]is very good [/I]at her profession. She has shown a that she can be trusted - even with her mistake. But we also have grown enough to know that we made the mistake of not talking about it and failing to take responsibility for our own treatment. So, we were wrong, too. She has worked with others. She does believe in the condition - she gave examples of others that she has treated. I believe, as do the other doms that she does have the training and the skill set required to treat it. Trusting ... well, as always is a choice.