I worked with a woman whose daughter had changed her name. She wasn't using the new name on the basis of "That isn't what I named her." I told her that we have the right to name someone.... until they're 18. After that, people are free to choose their own name. I followed that up with "It's disrespectful. You use my new name (I transitioned on the job), and I assure you that if you go back to calling me Mike, there's going to be a big to-do."
Now, I'm not saying that was what changed her mind, but she did start using her daughter's new name. Parents can be tricky. You'll always be their baby. But most of them do like to see us happily living our lives, and making our own decisions.

The tactic of saying "Who?" in a surprised tone every time your old name is mentioned seems to work pretty good, too.

Hugs, Devlyn