Cats can get very cold and could get themselves into a very dangerous situation.  It’s critical that all warm blooded animals maintain a certain body temperature and your cat is no exception.  If your cat stays outdoors for too long in very cold weather, she could lose so much body heat that it becomes life threatening.  If her gums are blue or she’s shivering violently, or she’s so cold that she’s barely breathing, she has hypothermia.  You need to get her warmed up, but not too quickly.  Take her to a small room and place her in her warm cat bed and wrap her in a cozy blanket.  Fill some bottles with warm water and tuck them in around her. Do not place anything hot up against her cold body as it could burn her.  If things don’t begin to improve, call your veterinarian right away.