Shelby spitting out her food repeatedly...:(

[Alllsmyls]

For the last two months my corn snake has been partially swallowing and then spitting out her food. She has been eating small frozen rats for a couple years now. I even went up to medium size but sometimes she would struggle with it so we went down to the smaller size. Two months ago I fed her as usual, she struck and started eating and had the rat 1/2 way down and it came back up. I waited a couple days and tried again. Same thing happened. She seems to be hunting in her cage. I know she is hungry. She strikes, spins, starts eating, then spits it back out. I have changed the brand of rats in case there was an issue with the first and that has not helped. I make sure the rats are warmed enough but not too hot. Please help!