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I'll give you things that can help get and won't hurt her. If this is a mild or low grade infection it may be enough for her to recover on her own.
Go to a store that sells reptile supplies and get a reptile night light. These are 75-100 watt blue, red, or ceramic bulbs that put out heat but not visible light. Set it up in a clamplight or desk lamp to the side of the cage where she can perch next to it or move away from it . You can leave it on 24/7 without disturbing their sleep. Radiant heat like that really helps sick birds to recover. You can crush fresh garlic and mix 1/4 clove per 8 ounces drinking water. It's a natural antibiotic and immune stimulant.
Offer her favorite foods for now to make sure she keeps eating.
In general you don't want to feed high fat foods like sunflower seeds or nuts . A pelletized diet or a cockatiel seed mix and vegetables is good. Dies she lay eggs?
As long as she doesn't lay eggs the cockatiel seed mix is fine and give a bird multivitamin in the drinking water at 1/4 strength what the label says so they'll drink it.
Whenever a bird Puffs out their feathers it means they feel chilled. Supplemental heat will help no matter how warm the house is if she's fluffed up like that.