On Sunday, the_local_echo and I drove over to see my mother and step-father for a post-Christmas lunch. Unfortunately I was just getting the worst of the symptoms of the cold from hell, so I spent much of the afternoon there asleep. Possibly partially as a result, I think my mother was being especially maternal, in the way she's always done when I'm ill.
However, I did notice later in the evening when my stepbrother and his wife came over and introduced me to my new niece (she is so lovely!), that my mother was talking about myself and my brother as babies, and effortlessly getting the pronouns right.
We'd planned to spend the night and leave the next morning. I felt too rough to leave straight away after a restless night, and ended up having a bath there. While I was in the bath, my mother walked into the bathroom and, for the first time, saw me naked with a female body. She didn't miss a beat.
I think she's really accepted, and got used to, the idea that she has a daughter. It feels good.