"You can't change who you are." - My mom, who is awesome.
Apparently she's suspected for most of my life and while she's not thrilled (as no parent would be) she understands.
It seems that not long ago my brother asked her if she thought I was transgender and her response to him was that if I was then I would say it when I was ready.
All I needed to do was clarify that gender identity != sexual orientation and the whole transgender being a spectrum thingy.
So, I feel better now that this huge weight has been lifted and I can be more honest.