How cold is cold? If you can tolerate it your bun is probably ok. They seem to prefer temperatures around 65*F. Consider offering your bun a blanket if you don't think they'll eat it or a cardboard box or something else they can hide out in.
As long as she has a place to get out of the cold (a carboard box filled with hay , you can put a cushion or a small blanket so that she can snuggle in it too) it should be fine if your rabbit is young and in good health and that it's not freezing (I hope for you it's not ^^).
My rabbits live outside, and we've been seeing temps in the 20s the past couple nights. They hop about all morning long and don't seem to mind it at all. Of course, they dug a nice snug den to keep warm in, and there is plenty of hay in the building I built for them, but I wouldn't worry about indoor temps.