I would not give her the antibiotics, and would give her the yogurt. I would also try to see if her droppings are the yellow from yolk, or yellowed feces. That's going to be the most important thing.
Yellow droppings (mostly yellowed urates, the 'white' crystals on top of the droppings and mixed in) can indicate liver involvement for one reason or another. there are a number of causes, including liver failure due to some other illness or condition that happened quickly.
It will be most important to make sure she's eating and drinking. She likely is too weak to so you must facilitate that. I would recommend mixing a little yogurt with water and boiled egg yolk, mixing that into some crumbles (a tiny amount) and trying to get her to eat that. If she doesn't, you can mix a little of that into some water and dribble it into the side of her beak. The "soup" with the crumbles and what not will give her a little nutrition and energy. You can even mix karo syrup or honey in both of the mixtures, or oatmeal ground to a powder in a food processor. Just make sure the oatmeal soaks really well before mixing it with either. Oatmeal or the karo/honey will give her some more quickly accessed energy to hopefully fuel her to eat.
However, the most important thing will be to determine some other symptoms so we can figure this out if she makes it through the night - and even if she doesn't.
First, tonight, check her thoroughly for any signs of mite infestation or lice. Check carefully in the most moist/warm areas (under the wing, back of the neck, near the vent). We must rule out parasite infections which can take her down and make her anemic very quickly.
Also feel her weight - is she heavy in her chest/keel bone area, or emaciated? Is she very heavy and lumpy in her abdomen between her legs (feel very delicately in case of a softshelled egg) or is she hard there? Does her crop feel empty or full? Are her combs moist and waxy, or shrivled and scaley? Any signs of broken skin, redness around the vent, labored breathing, etc?
