My winters are also long and cold. I built a heated night box in the back of a greenhouse. A 100 pound Sulcata really can't be kept in the house. They are destructive. There are many options though, and you have time until she is big enough to tear down walls. A night box works really well in summer. Yvonne posted some links above to show you what I am talking about. Best of luck. Remember to ask any questions you have.