OK - well I talked to her on the phone, and that was much less awful than I expected!
I didn't make a final decision yet, because I want to talk to my T (on Monday) about it. But, she seemed nice enough and answered all my questions.
Basically, she said for intake that it's for her to get to know me, so that she's not putting me in a group without knowing anything about me, and for me to get to know her and ask questions. She also said she uses it to tailor the group content a little. She said sometimes it's to determine if someone can benefit from the group, but for DBT - if you're therapist is recommending it, then it's 95% certain you'll benefit.
I didn't ask specifically if she was going to grill me over symptoms or history though!
And, I asked whether self-disclosure was required in the group, and she said "no" (and it says on the website that you don't have to talk if you're not comfortable).
The only thing that really worries me is that you have to sign a release at the intake for her to talk with your therapist.

This makes me really strangely uncomfortable. I guess if she's giving my T info - and it's just one way - I can live with that (my T should probably have as much info as possible to help me). But I don't want him sharing info about me. That feels really icky to me, and like it's going to screw up my ability to feel safe and share with him

.
So, I guess I know what I need to talk to him about next week.
Thanks for the advice, and for listening, and letting me work this all out here! Ahhh I feel like I really want to duck out and grab chocolate now! (I'm trying to be good, but that was really hard and stressful for me!!!)

Thanks!!!!