Straw bedding is an excellent insulator if you have it I would bed with that.Very helpful.
I think I will adjust my cut off to bringing her in when we hit the teens rather than single digits which will be several nights this week.
I would bring her into the garage and put cardboard boxes around her because I think there are drafts underneath the garage doors (or maybe put her container in a wheel barrow so there is some draft protection all around).
The garage is unheated - at single digits outside I had an issue with the utility sink faucet freezing so I will have a small (750W) heater under the utility sink. I doubt it will make a huge difference to the area as a whole.
I could move her into the mud room which gets down to about 35 degrees when it is single digits - but again I am worried about a utility sink freezing so I may put a little heater under that sink too. Garage probably best and I will put a thermometer in there so I know what temperatures she was experiencing.