She's giving herself a dust bath. Yes, normal healthy chicken behavior. The first time I saw my chickens rolling around in deep, dry sand I thought they were dying. They were rolling around almost on their backs, slowly and thoroughly relishing it.
I can't believe this horrible weather we are having. I'm originally from Canada and am used to snow storms and bad driving conditions but I'll tell you, this winter has had more dangerous driving days (ice) where I am just north of San Antonio than I remember any winter having in Toronto. (Yes, my home town is the city with the ridiculous mayor that has made all the late-night comedy shows as well as national US news. Honest, Toronto is a really safe city although you wouldn't get that impression judging from the mayor's associates.)