You're luck being 18, and you're right do what you have to do for yourself,
and she'll learn to accept everything at her own pace as well.
From what you've said I'm sure she'll come around, just be patient

I'd say don't keep her in the dark with your transition.
If you're going to the therapist, or the doctor just tell her real fast.
That way she'll be transitioning with you and that helps.
I tell my parents everything regarding my transition; they know all my appointments, my future goals, all that.
This way there's no surprises and they feel included in my journey.
And about your dad,
A lot of the time, if one parent accept their child being trans,
the other will slowly follow. So don't lose hope in your dad.
Everything should be fine!