From what you've shared, this therapist doesn't seem willing or able to help you work through your issues/grief over no mothering. If all she does is trigger those issues, without helping you, then it does seem like a healthier option to put some distance between you.

Only you can decide how the lack of a mother impacts your quality of life. It might be worth talking to another therapist about it, either one who isn't so much like your mother or one who can handle and work through your transference without trying to be the mother you lacked; in other words, someone who can help you help yourself rather than try to fulfill those needs.

Whatever you decide, I do think this therapist has done you a favor by not trying to do something she can't and then end up causing you more problems through rejection.