Welcome to the forum from a fellow Albertan (okay, I'm a recent addition).
I hope the vet has an answer for you. If she is eating and drinking well (sounds like she is) then there must be another cause.
Did you own her last winter? What can you tell us about her history? Has she a good natural coat and plenty of wind shelter? What breed is she? Lots more information for us might prompt more suggestions, but I'm interested in what the vet says.