Give her chopped hard-boiled or microwaved egg. Most sick birds will eat this.
Another good food is a hand rearing formula for caged birds. Kaytee Exact and Nekton Tonic K are good. We have saved many weak chicks and adults with Nekton Tonic K. You can get these at a local pet supply house or at Doctors Foster & Smith 800-381-7179.
You will need to use an eyedropper to feed this to her. Be careful to place the eyedropper far back in the mouth. There is a hole at the base of the tongue that leads to her lungs. Get water in there and you will make things worse.
Nathalie (ThreeHorses) suggests the following:
If you don't see her eating as much as you like, you can always wet the crumbles down a bit to help her swallow while she's weak.
Put some oatmeal in a coffee grinder, grind it to tiny consistency, put it in some very hot water, and let it steep until it is mostly oat water. Mix that with a pinch of crumbles and fed that to the bird so that when it swallows, it essentially souped up water.
Feed her beneficial bacteria (lactobacillus), they keep digestion going correctly and fight disease by crowding out disease bacteria. You can just mix 1-2 teaspoons of ACTIVE culture yogurt with a small amount of food and give this as the only food until she eats it. You can also buy lactobacillus at health food stores, pharmacies, Wal-Mart, and Lake's Unlimited 800-634-2473.
If she is not eating well, you can try tempting her with treats, chopped grapes, chopped hard boiled egg, and yogurt mixed with crumbles (mushy texture, not soupy) are all good things to try. The hard-boiled egg gives her protein that gives her energy to recuperate. Yogurt gives her good bacteria inside her digestive system to help fight and overcome bad bacteria that might have gotten a hold of her.
If she is not eating at all, you might try feeling her crop (by her throat but down near her chest) and see if it is very full and hard. This usually means she has eaten something that is not being broken down and it is either blocking her or is decomposing in her crop and thus poisoning her. If that's the case, she will need her crop cleaned out.
If she will eat on her own, make sure she has fresh water to drink. You can add Pedialyte to her water, this will help keep her energized and hydrated. You can by it at any grocery store in the baby section. (It's usually given to sick babies). Dip her beak in it (gently, don't or drop a little on her beak with an eyedropper. She will lick it off as it rolls down her beak.
If she has eaten something bad you can use an eyedropper to give her molasses water, about 1/2 teaspoon to a cup of water. This is sweet so she will like it, and it will help flush her system of toxins. The sugar in it will give her energy.
You can also try red Jell-O in the water. It doesn't provide any nutritive help like Pedialyte does, but does give her sugar for energy. The red color helps make it attractive to her (red draws their attention) If she's sick I'd opt for the Pedialyte.