It sounds like your girl is suffering from feline herpes. This is fairly common in cats that come from shelters or who are late receiving their vaccinations. Unfortunately, there is no real treatment for it, but you can give her a supplement that often helps prevent the problem or make the symptoms less severe. If you put 1/2 teaspoon of l-lysine in some canned food every day, this will help build up her immune system and she should have fewer symptoms as time goes by.
http://www.papanature.com/store/ProductDetails.aspx?c=Herbs&pid=NOW-00240
The other possibility is that she may have nasal polyps that are causing the chronic nasal problems. Your vet can run a small scope up her nose and see if there is a polyp in the nose. He can remove it and that will also take care of the problem.
Please let me know if I can help further.
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments