Each dog, like each person will have a different tolerance for cold–and as with people, some dogs are just bigger wimps and whiners, LOL.
I know Keoki is more bothered physically by cold than Jazz is. We have to pay attention to him, because he will shiver and whine, but won't stop investigating things. I have to watch to determine when he really needs to get out of the cold. Jazz doesn't fuss until it is in the low 20's.
If you 're just taking her out to potty, then probably any jacket you can get from Walmart, etc will do. It's just needed to keep the edge off for a few minutes.