I think that by being caring and making a connection and being in a parent like role therapists allow us to reconnect to our young need to be loved and cared for, but at the same time this need will never be fulfilled, the therapist is not our parent, whatever they offer us will never fully meet our old need to be taken care of completely. So I think that's why it hurts. She's bringing out a neediness in you (that exists because your mom didn't do a good enough job and because it was never fulfilled in childhood) and then not fulfilling that neediness, because she can't, no one can. What you're supposed to do is fully mourn the loss to move forward, and what you'll want to do is anything other than acknowledging and mourning.