I'd be very surprised if your t diagnosed your mom today. S/he is there for your own treatment and this is just a part of it.
And yes, it does sound like your mom has been practicing. And/or she genuinely sees the conflict between you and is working on it in her own way. You might never hear her admit it though and she might not even be aware of it on a conscious level.
My personal experience? At my BPDmo urging at age 14 we went. She ended second or third session early, was upset w the therapist for not scolding me enough (she thought she was "siding" with me) and we never returned. The second and last time was a family meeting while my BPDmo was inpt psych. This time the therapist seemed very much to have been taken in by my BPDmo charming personality and was kinda hard on my Grams while I was very quiet. I found it useless. At least my BPDmo seemed to get some validation from it but obviously not enough since she spent the next 5 yrs writing about how sane she was and that caffeine made her ccrazy. No changes made. No personal responsibility taken.
Honestly it has a lot to do w the skills and experience of the T imo, so don't be nervous and let what happens happen!
Good luck!
