Patience and encouragement.
I don't see the difference between whether the beginner is a guy or a girl, I think it's strange that this differentiation has been made by the OP.
Anyway, I'd suggest the main thing to do is keep her warm and dry. Nothing ruins a new activity more than being uncomfortable while trying to learn it, make sure she has decent enough clothing to protect her from the elements.
I think you have to know the person as well and go with how you think they'd most like to go about the day. Figure this stuff out ahead of time so there's no issue when you're at the hill. An example would how she is taught, some would see you arranging lessons as a helpful start with someone who's knowledgeable and a trained teacher, other might see it as you abandoning her to go have fun by yourself. Really push for the lesson, it'll get her started on the right path.
Encourage her to fall on her butt if she has to fall, that is the best place to take the impact.
If you have a skateboard get her on that for her to somewhat understand the sensation of going sideways and turning.
Go for one day to start with, she may either hate the whole thing or love it but needs to rest her bruises.
If she doesn't want to do it anymore then get of the mountain, let her be the one to call it a day if she's had enough.
I hope that helps.