Is your wife seeing an individual therapist in addition to joint counseling? I would agree that she should see her own therapist either before or in addition to marriage counseling.

I would be very wary of any therapist that is completely against drug treatments or denies the existence of bpd. If the t was wary of psych drugs that sounds reasonable. Or wary of the stigmatizing effects of a bpd diagnosis then that sounds reasonable too. Any extremes I do not trust.

You have a right to have your own boundaries. If you are not up for endless argument sessions you have a right to cut them short. If your wife wants to cut someone out of her life that only applies to her it does not have to apply to you. If this therapist is saying otherwise, run!