For what it's worth I think it would be a shame for people to start wearing helmets whilst skiing as a knee jerk reaction to this tragic accident.
Statistically you've a 1000000-1 risk of being killed on the slopes, all sports carry their risks and that's a pretty tiny one isn't it ?
I've been skiing for 30 odd years and every time I've had an incident, I think without exception is from other skiers ploughing into me at speed from behind and generally you hear them coming and are prepared, albeit at the last moment, were I wearing a helmet I'd probably not hear them coming !?
That being said, now that I'm using Warfarin I'll probably start to wear one anyway, but definately dont think anyone not using it should worry themselves... This lady sadly got very very unlucky 1000000-1 unlucky !
The western world wants everyone wrapped up in cotton wool these days and I think it's a shame, without risk there's no thrill and without a degree of danger people are more careless.