Wow. I don't understand how that is even possible. I don't know about you but our host person puts like maximum effort into not switching and is only ever successful at that until a trigger comes along and then she is gone. It happens multiple times a day out of therapy and multiple times a day IN therapy so she/we just couldn't do that. It would literally be impossible for her.
I really don't know how your therapist can expect that of you, and wonder if she even understands DID because if she did surely she wouldn't have that expectation. Or maybe I am missing something here??

Anyway my T talks to whoever is present. She acknowledges whoever is present if they want to be acknowledged and she never ever asks for any one of us to step forward or step back.

I am sorry that your therapist takes that approach, I know it definitely wouldn't work for us simply because we could not meet that standard no matter how hard we tried to.