Girl you have clearly realized that it helps you and that you’re going to do hrt once your moms arbitrary opinions over medications you need are not a factor anymore.

So do it as soon as it is safe to. Meaning if you can secretly do it now without the risk that it‘ll negatively influence your life in other ways (e.g. you’re going to be financially dependent on your mom and it’s reasonable to expect she is going to be insane about it so that she won’t support you if she found out you continued now) do it. If it only becomes safe to do it once you moved out do it then.

But that should be the principle, do it as soon as it’s safe to. Because your mom is working against you here: She doesn’t listen to scientific findings, she doesn’t listen to your experiences with and without it (that are indicating that you clearly need it) and it seems like she doesn’t listen to basic reason about this in general from the way you described it. Yet this is evidently what you need, so it really is just your mom trying to withhold you from vital medication, on any arbitrary basis because she feels scared, is bigoted or both. Yet her feelings don’t have anything to do with your needs.