At almost all animal shelters, rescues and SPCA's, there is one commonality when you take the cat home. No matter how clean the shelter is or how well maintained, most of the cats will go home with respiratory illnesses.
Some cats get over it on their own while others need antibiotics. Keep a close eye on the secretions from the nose and eyes. If they are green or yellow, the problem has now changed from viral (cold) to bacterial (infection). If the problem is bacterial, it will probably not resolve without antibiotics.
If she is congested, you can use warm saline to wash the eyes and pediatric nasal saline drops to help clear mucus from the nose. You can also run a humidifier. Be sure to keep her hydrated by using plain pedialyte. And be sure that she's eating.
Then see your vet if this does not improve.
I hope this helps!
Let me know if you still have questions.