Eeek! I'd feel the same way! Some of what I think I pay for in therapy is for someone to totally be on MY side. I sensed an element of your therapist trying to appease her and you, when I would have wanted him firmly in your camp! It must have felt like he played right into her hands. And yuck, to mention the dreaded end of therapy I can't imagine how in the world that could be helpful.

Do you want your Mom to attend a session with you? Why is your T eager for that? I think the two of you need to have a lot of discussions about that before you allow that to happen if this is any indication. Therapy should be focused on you and your healing, IMHO. I think your instincts about her are right on the money.