I wear a Smith Variant. Not Women's specific, but I like it. I have a feeling "women's specific helmets" only refers to the color schemes
As for sizing, I'd recommend going to a shop and trying them on. Mine is adjustable, but I wear it all the way tight and it leaves me room to wear something underneath, like a balaclava. But so far I haven't had to, as the helmet keeps me plenty warm.
Snowsport helmets have ear pads that will keep your ears warm.