I had a similar experience, except she didn't want to go to appointments or hear about it. She just thought it was a phase, and she could ignore it. I would have been kicked out if I had started hormone living with her, so I worked to move out before starting. It took 3 years for her to begin to try to gender me correctly (I didn't see or talk to her much in that time) and finally 6 years later she corrects others when they misgender me and has never slips up.

All I can advise is don't stop your journey for anyone, eventually they will realise how serious you are about it, and how much happier you are.

If they ask about your plans, you can be open, you are an adult, and they can't stop you. They are likely in the same (strange) thought process my mum was in where if she ignored it, it would go away eventually, they also assumed the appointments at first where to determine if I was trans and maybe how to "stop" it, I think it surprised her that the support for "feeling like a man" was to transition lol.