^Agree with this. Nothing more to add.She will have to see a vet and probably have it surgically removed and the sooner the better to be honest. They would need to x ray her first to see where it is now so as they can get to it but it will have to be taken out otherwise it can cause a blockage and kill her later. Are you sure she definitely swallowed it? they're a rather strange shape to go down the throat I would have thought and can only imagine it's one of the one peg or two peg pieces.
I hope she's okay and I hope your son isn't too upset by it all as accidents happen and I know how bad we can feel about them.
Please let us know how she gets on.