Some cats vomit with great regularity, Samantha made a hobby of it a few years ago. I took her to the vet and there was nothing wrong with her.
I would watch for other symptoms indicating problems, such as hot ears (temperature) or if her scruff remains standing when you gently pull it upwards, instead of springing back to place (dehydration). If she also has diarrohea, then she may have a tummy bug which is worth having investigating by vet.
If she eating well and playing, that indicates that there may not be a major problem, but always best to err on side of caution until you've got lots of practise in spotting poorly pusscats.