Jennifer, this is an interesting topic.
I don't know how much you've looked into this or have practiced. You may know more about it than I do. I've read that everyone's voice can deepen somewhat as they age, so it is something that I am concerned about and I try to do voice exercises as much as possible. Some of the exercises are fun too...like singing:) I noticed that there are links to voice training articles and videos here on TGGuide. If you are interested, I could also share links to some of my favorites videos also.
So, just in case you haven't yet taken the step to voice feminization, here are some of the basics as I know them. There are a lot of ways to feminize the voice, pitch is just one part of it. There are many things that together make a voice sound believably feminine...resonance, tone, etc. Woman also have a beautiful kind of singing voice quality and vary pitch and emphasis more within words from syllable to syllable. Basically, women talk more in their mouth and head than their throat or chest. They even move their mouths differently while speaking. I've read that it is easier for the deaf to read women's lips than men's because of this.
As for seeing the opposite gender in the mirror, does that mean everyone, or transgenders? I can say that there is truth to that, at least for me. I can't say though if it was just me subconsciously focusing on characteristics that are feminine and ignoring anything that might be considered masculine or something else. Maybe I am just seeing how I want to be seen, or the way that I feel inside.