If your cat has vomited and is playing and showing no signs of physical discomfort, it is most likely nothing to worry about. Just keep an eye on the cat to make sure there are no other signs of a possible illness. If however it is not an isolated incidence or there is blood in the vomit, or even more important, the appearance of what looks like coffee grinds(blood!) , or any signs of poisoning, or if kitty seems really sick before or after get her to the vet asap! also, is there an diarrhea, constipation,dehydration or weight loss?