What a lovely cat!

Is your garage heated, or is there a warm corner? You could fill a box or crate with old blankets, and have her food and water near there, to encourage nesting. Momcats usually nest where THEY want to, but sometimes will use a ready made one.

Good luck! That's going to be a late litter; as such will be easy to place since kittens are scarce in the late fall and winter.