People also forget that hay is an amazing insulator. Give that inside her sleeping area and give loads of paper bedding (even buy super cheap loo roll) that and the shavings on the bottom in a nice thick layer for her to borrow down in will keep her nice and warm.
If she keeps sleeping in the tubes take them away as she may be warm when she falls alseep but at you can imagine she will get colder and colder as she is asleep.
I also give more soft bedding every few days so they can re line thier nests after sleeping on it and flattening it down.
Aswell as their main nest/house I also give them smaller huts/dens filled with soft bedding encase they want to sleep in a warmer spot.
Hope this helps
xx