I'm going to be on the wrong side of this discussion
Oragejuice, you are a wonderful friend and I'm glad you care about the safety of your room mate, but whether or not she wears a helmet is none of your business.
Don't get me wrong, I'm a helmet advocate!
I'll give you a couple of my real life scenarios:
One:
I ski with some friends here in Michigan who never wore/wear helmets. Within the past few years a few of them have moved over to the helmet wearing side of the hill, while a few others still don't/won't wear a helmet.
I may, casually mention that I think they would love a helmet if they tried it, and even encourage them but if they say no, I drop it. None of my business!
Two:
Epic Friends -
Many of the best skiers I spend time with from epic don't wear a helmet. Cgeib, Bob Barnes, nolo, Robin Barnes, to mention a few. I hold these folks in very high regard, and don't even give a second thought to their choice of helmet or no helmet when I'm skiing with them. Heck, I can't keep up with them long enough to notice what they have on their head(s).
If I were to be pushy about helmet use with my non helmet wearing friends, I think I would likely miss out on some great times with them.
Love your room mate, suggest a helmet, even offer her the chance to try yours, but don't push it. If you push it, then you are a know-it-all

Most of all, enjoy your time with her on the slopes whether she wears a helmet or not.
