Hello and welcome to Just Answer. I am a licensed veterinarian and would be happy to answer your questions.
How old is your cat?
Is she an indoor only cat or is she allowed outdoors?
There are very many reasons why cats vomit, some more serious than others. Vomiting is a vague sign that can be associated with simple things like dietary indiscretion to more serious things like intestinal obstruction or metabolic disorders. In young cats, we usually are a little more worried about foreign body ingestion. We decide how aggressive we need to be in diagnosing and treating it based on how severe the symptoms and how long it has been going on.
In her case, since this has already been going on for a few days without resolution and since it is affecting her appetite and activity, I would seek veterinary intervention at least for an exam. There is a lot of information that can be gained by a thorough physical exam and based the findings, they can decide what is the next best step. She may need some sort of fluid therapy or injectable medications to control the vomiting as well as further diagnostics like bloodwork or x rays.
In the meantime, you can try to give some hairball medicine to make sure that hairballs are not a contributing factor, although they rarely are the sole cause of a vomiting problem. I hope this information is useful. Please let me know if further questions.