My internal voice is and has been 100% female all along since I knew how to talk.
I have had voice surgery and I sound 100% female, 24x7, coughs, sneezes, laughter, grunts, everything.
People postop from voice surgery say that when they start to talk they are startled by their new voice and their brain kind of doesn't recognize it. Not me. This is my voice, and it was pretty natural when I was able to make a sound again.