I'm sorry this is happening MPD. I know exactly how hard dissociation can be, it's one of DD2's challenges. You have all my support from over here and I will keep you all in my thoughts
DD2 also has a dissociative personality, and whilst things did get better some after she had therapy, she still dissociates occasionally (thankfully not frequently) and I guess she may always at certain times to some extent, but I remain hopeful she can improve further. It's very PTSD related for her, there are certain trigers (some predictable that I know about, others not so) that can make her dissociate, and meltdown in a blank panic and she will often have amnesia afterwards and not remember the total meltdown at all.
I wonder what prompted your DD to share with her friends? Has she done anything like that in the past?
How much does the therapy you do touch on her past? I know some children can't cope as well as others with talking about it but the biggest improvement my DD2 had with her dissociation was after she did EMDR therapy, which was all about going through her past memories and trying to get her brain to process them properly so they became more like bad memories and not retraumatising flashbacks which panicked her. It won't work with a child who can't open up enough to share their experiences, or a child who is constantly trying to manipulate or lie to professionals, but I wonder because your DD seems willing to share her past, whether that kind of therapy might help her?
For us, sadly the only thing that helps when DD2 is going through an anxious period (eg. transitions, big routine changes, anniversaries etc) where her anxieties are making her very clingy and want control (and dissocatie more frequently) and are really interfering with life, is just to 'lockdown'. Small calm world without too much sensory input from anywhere. Very predictable routine which barely changes. Lots of talk about being safe. That doesn't cure anything but it minimises until we can ride it out
The other thing that has lessened not so much the dissocative episodes, but has definitely lessened her agitation and general anxieties, and also her aggression is medication - she takes Risperidone right now, and I'm glad she's on it, it's a significant improvement in her day to day functioning. However her anxieties are always there, she isn't normally a confident and non-anxious person who has bad blips.
With the controlling behaviour, there's two main approaches, you can remove as much choice from her as you can, or give her lots of choices over small things. I guess by now you know what works better for your DD, and whether she responds better to having no choice or lots of little choices where appropriate.
I have to say that the fact your DD has become generally so confident and independent is a testimony to your amazing parenting. You are doing a fantastic job and whilst you can't wave a wand and make this go away, you really have made such a huge difference in her life, so try to never let yourself believe you are a useless parent
I hope this period ends soon and you can get back on track again