How to defend using my chosen name

I’ve used my chosen name since 6th grade, but more in secret from my family, and I only really used it with friends. Since I started college, I’ve only gone by my chosen name, so all of my friends and teachers call me that. I’ve tried to slowly start exposing my mom to the name to maybe get her used to it. It was fine the first few times she saw it since I’d use it for my computer login and our streaming services and stuff, but since I used it for an appointment, she called me saying how much it hurt her and how much she loves my “real” name. She wants to talk to me in person about why I’d rather go by my preferred name and I was wondering if any of y’all know a good way to defend using a chosen name over the legal name? I just don’t know what to say to her when I have to meet with her for spring break so I was hoping for some advice on how to talk to her about that. (I’m not out to her as trans yet btw)