M.C.
Could you make a sheltered area outside for her to poop in? It shouldn't be too difficult to put up a roof and a couple walls. That way, she won't have to stand in the snow to go, and will be protected from cold wind. You could even buy some jumbo wee-pads to take outside with you each time so that she has a warmer spot to stand on. It would also come in handy to provide a shady spot for her in the summer.
I would hate the idea of getting her into the habit of going inside... I get that you are doing it out of desperation for her at the moment, but big dog= big poop! Lol.