Is your garage heated? If it is then I would not bring her in at night. Unless you want her to stay in the garage all winter. The shock of going from warm garage to fridgid cold winters can be very stressful. We live in northern MN and have similar weather to yours. Your duck house sounds nice and snug, some ventilation is good up near the roof, like Miss Lydia said. And, keep a lot of straw in there so she can snuggle down and keep herself warm. There have been a few times where we've needed to bring a bird into our garage (heated) to treat it for injuries or if they're *really* having a hard time with the cold. If they stay inside for any length of time (overnight or longer) then I'm always very careful about when I put them back outside. You know how it is, when you walk out of the house on a cold day and the first few minutes are the worst until you start to adjust to the cold.
If your garage is unheated and you do decide to bring her in make sure the crate is well bedded because the garage won't be that much warmer than her house is. But, it might be a good option on those days with crazy cold windchill or if there's a blizzard coming.
