Pregnant stray outside for winter

A few months ago I picked up a stray off the side of the highway. I was worried she'd get hit so I took her home. She's doing great now... we' got rid of her worms and she's a healthy weight, however, I have come to realize she is pregnant. I've tried to bring her inside, but she is aggressive toward my indoor cat. I supply her food and water in the garage and she often sleeps in there. But with the temperature being 5 to 14° tonight I'm wondering if it's too cold. We are expecting 3 to 5 inches of snow, and I don't want her to freeze especially since she's pregnant. I really cannot bring her inside for fear of her attacking the other cat. Does anyone think that the garage will be too cold for her? What are some things I can do to supply a little extra warmth?

Is it possible to keep her in the bathroom or a spare room?

How did you get rid of her worms?  I don't know if it might be dangerous for the kittens if you gave the mom medicine? Maybe call a vet and ask or maybe someone else will chime in on here. 

If you want to keep her in the garage, you can make a cheap insulated shelter with a plastic storage container with a hole cut into it and some straw.  Good luck.  

is this an attached or unattached garage?

do you have a heating pad she can get on and off of? or maybe a lamp she can get under? any bulb that gives off heat would help.also, a cardboard box or styrofoam cooler with a hole cut out for a door. maybe a small space heater on low heat. 

She may be a little aggressive because she is pregnant - they get protective.  I second the advice above.  If you cant give her her own room, get her any sort of shelter and fill it with straw.  In fact, I'd put two or three in the garage and allow her to choose her favorite.  Expectant mothers can be fussy about their nests.

Feed her plenty of wet kitten food - she needs the extra calories now. Now would be a good time to start spending time with her, so you will be able to socialize the kittens and find them good homes.  Perhaps you can contact a rescue and see if they can make suggestions.

Thank you for caring for her. 

A spare room is ideal if you have room. I have one feral who got hypothermia on her paws last year and won't leave my room. She's comfortable and happy in there. If not, the garage will protect her from the elements. Make sure she has plenty of food, water and a litter box so she does'nt feel the need to leave often. Like someone else suggested a heating pad on low would really help.