While my first impulse was to say "go in male mode", like most everyone else in here has said - I had a thought I figure I'll share...
I don't know your wardrobe, but do you have some women's clothing that could serve while in male mode (slacks, top, that sort of thing)?
That way, you could still go as a "guy", but when the topic comes up (which it almost certainly will), You could admit that yes, these ARE women's slacks (or whatever).
In this instance, if it were me (if only!), I'd almost certainly be wearing panties - in case things proceed that far, she gets a little extra treat!?!?
Whatever you do, treat this lady like the jewel she seems to be, and good luck!!!
