Why is my baby robin breathing so hard!!!!!?

there was a robin that decided to put its nest right in front of a cats house.The cats love to eat birds.I find it eating them all the time.So i kept an eye out for the cat to make sure it dousnt eat any of the baby robins.Soon after that i came to check up on them and the babies and mother were all gone!They were way to little to fly yet.They didnt even have all of thier feathers yet.Then i heard some chirping near by.Thier was one little robin in the bushes just waiting to get eaten by the cat.The mom was no where to be found so i took it home fed it some food and everything.There is no rehabilitor place near me that i can go to to help save the baby robin!i have been feading it dog canned food with liver and beef in it and mixing water into the food, i just put a hot waterbottle on it with a cloth on top for it dousnt get burned.The first day and the second day was fine but know she is hardly satnding up!She is also breathing very deeply! i dont know whats wrong!