How to tell my sister I'm starting to medically transition

I (20FTM) have been living as male since 16, pre everything. My twin sister and I used to be very close, but my parents got to her with their transphobia immediately and she and I stopped talking pretty much entirely. A few months ago, we became very close again, more so than ever. We don't talk about me being trans, but my friends and gf call me he/him and by name in front of her and she doesn't flinch or get upset. She'll write down my name if needed but hasn't used it really. So she's not actively unsupportive anymore, but I don't know if she's actually supportive now. How do I tell her I have a top surgery and HRT consult without ruining our relationship? I know many of you will think that if she's unsupportive I should cut her off, but she's my best friend and I want it to go as well as it can. If I have her semi-support, I'll be more likely to have my parents' too.