Please answer some of these questions & I can "try" to give ideas as to what might be wrong. But regardless, she does need to see a vet anyways.

Age?
How long have you had her?
Where did you get her?
How long has she been ill?
What food was she on at, where ever you got her?
What food is she on right now?
Is she coughing?
Is there thing coming out of her nose?
Is it clear, green or yellow?
Is it runny or thick?
Is she drinking any water?
Is she eating all the food the bag said she should be eating?