Hey, I would just talk it out with her. My mom does the same thing; she says she supports me, but she doesn't agree with it. lol. The trick is to do small changes in front of her and not all at once. If you do dress up in front of her, it's a big change and she needs some time to adjust to that. Again talk it out, try not to get too emotional about it. If you feel that she is starting to get heated up, calm her down a little bit before you continue. If she still doesn't understand the point of the medication, explain its a dysphoria and your transitioning to treat this. That you need to increase because your levels are low and the effects (and affects lol.) aren't going to work 100%.
I wish you luck.