pachyderm, your therapist is not your mother and, presumably, didn't know your mother so the "reminders" are coming from your head/thinking. Too, what your mother did is in the past and your therapist is in the present. That's why therapists are so good for us, they can help us sort out what was past/mother and present/whomever so we don't continue to confuse them.

My mother died when I was 3 and my father remarried when I was 5. I wanted a mother very badly and "fused" my mother and stepmother together only my stepmother and I weren't a good match. It took 10+ years of therapy to "sort out" which mother was which (I didn't have a "name"/know what to call my natural mother and could not refer to my stepmother as "stepmother" (she was "Mom" or "my mother")) and get out from "under" my stepmother's forceful (putting it mildly) influence so that I could see what I wanted and run my own life without all the confusion of not knowing what was "mine"/my idea or thought and which my stepmother's influence and beliefs/ways of doing things.