Just to throw a twist into the conversation, but what if she was a passing pre-op trans woman too!
Just my opinion on the topic, if you're just hanging out with friends and being flirty there's no need to disclose. But if there's one on one time, like a date, where there's a chance if intimacy, then you might want to bring it up. Relationships are a two way street and you can't keep the truth from her in fear of a negative reaction. Yes, you are a woman with "the wrong plumbing", but if she's not accepting of it, you can't make her be accepting.
Personally, I'm not even considering a relationship at this early point of my transition. I don't pass, probably never will. (I wish I had your dilemmas.) I just don't feel I can give a relationship effort when I'm too busy trying to fix all my broken parts.