I agree that you should NEVER give chicks or chickens a lot of onion. I gave my leghorn onion (not too much) and she seemed fine. I'm still pretty confused why people are saying that you should not give your chickens uncooked rice. I give my chickens uncooked rice and they seem okay. I also gave it to them as chicks and they also seemed fine.Did the OP’s chicken get uncooked rice or cooked rice? Uncooked rice should never ever be given. Onions and garlic should not be given to chickens or other animals because those may cause liver toxicity and anemia, if given in large quantities.
Chickens need a balanced diet in a commercial chicken feed. Either a flock raiser/all flock feed or a layer feed for layers should be used. If other things are fed in quantities, there would be a lack of protein, vitamins, and minerals. I have fed a small quantity of cooked rice a couple of times, but uncooked rice could possibly swell and block the crop or digestive tract.