Snowfox has it right. If the board length is suitable to her weight and skill level, she'd be fine on a men's board. They are wider and stiffer (that's what she said), so lacking the power necessary to turn a stiff men's board or lacking the foot size for the waist would be two possible problems with a men's board. I have tiny feet and can't ride most women's boards, so I know first hand how foot size affects riding ability. Just have her measure her foot across the width of the waist to make sure it's a good fit (they should be about the same size).
That being said, men dominate the snowboarding scene, so I always suggest that women buy products made for women. The more we support that side of the industry, the more products will be available to us. It's pretty stupid for her to want a men's board because she doesn't like "pink girly sh*t" - there are PLENTY of women's boards out there with sick graphics. Check out the 2011 Never Summer and Arbor lines, for example.
Anyway, plenty of ladies ride the Skate Banana narrow.