People withhold a lot of things from their therapists, and therapists know this. I'm not sure that you have to share everything or even be honest all the time. Doing what feels right in the moment is perfectly fine. We are all doing the best that we can. And that is true for the therapist. So if she is off sometimes, well, she is only human and not inside your head so some suggestions may not be perfect or suitable. You could choose to say so, or not say anything and just disregard it. It is really up to you. You are her boss, remember. She works for you so you are more in charge really though it may not feel that way.

If the groups seemed better than expected, then I'm not sure why you would not want to go. You sound like you want to feel better and work on stuff and that sounds strong in your post so the best thing to do is go ahead and go through with it. Of course you are going to feel some resistance, but maybe it is like getting into a pool. There's that hesitation at the beginning and so you go back and forth about whether you want to get wet. Some people dip, some dive, some wade. Whatever works best. And again determined by you. Good luck with this. BPD is difficult, but lots can be done to help with it.