It sounds like she has a respiratory disease/infection. If possible, I'd isolate her from the other birds. Keep her warm and out of drafts. Give some electrolytes if you can, and vitamins (you should be able to find electrolytes at a feed store). Make sure that she is eating and drinking-- if a bird doesn't eat or drink, it will get weaker and be less able to fight off a disease.
If you don't notice improvement within a few days, get some antibiotics. In fact, it may be a good idea to get some now, just in case. Water soluable antibiotics like oxytetraycline, Duramycin, and Terramycin may help. Tylan50 is probably the best antibiotic for respiratory diseases, but it is given as an injection (usually-- there is a water soluable version, but its harder to find). Antibiotics will help a respiratory disease if it is caused by a bacteria, but will not directly help if it is viral-caused. However, even if its a virus, antibiotics can help by preventing a secondary bacterial infection from forming.
