As big as a goose egg is I don't know if a cat could do much with one. They are pretty tough to so don't think a cat could break one open either. I'd keep a close eye on the prolaspe you don't want it to dry out at all, keep it moist and hopefully it will go in on its own. Does she eat layer or do you give oyster shell on the side? I don't feed layer because i don't want my boys to eat it, so i feed oyster shell separately.I've searched all over the pen and have not found a trace of an egg but I do let them free range quite often so it very well could be anywhere. Do cats steal eggs? Because we have a huge stray cat population around here.