I hate this time of year. It really is disgusting around here now. The roads are going to be nothing but black ice everywhere for the next couple days.
I think if you're good to go for a walk, I'm sure they can go. Let her out in the backyard as long as you're there to let them back in. I wouldn't just leave her out there alone for hours without shelter.
I like to go out to empty baseball fields with a baseball bat and just hit balls around no matter what the temperature is. They're both usually huffing and puffing after 20 minutes of chasing around balls. It's good exercise where you don't have to be outside for hours in freezing temperatures.
Having one of these helps too.