Hairballs are overrated as a problem in cats. A true hairball is hair wrapped in saliva and requires no treatment. Hairballs almost never cause illness in pet cats.
On the other hand we should see your cat if she vomits frequently - whatever the vomitus is! If she is turning her nose up at her dinner or hiding then we should see her as soon as possible. Normal cats eat several times a day so even a single day of poor appetite is significant.
If she vomits a lot but doesn’t feel poorly she may still have a problem. Some cats are very sensitive to specific proteins like chicken, beef or lamb. A change to a diet free of the common proteins that cause hypersensitivity or to one that is specially treated to reduce reactions often helps these cats.
Often the only sign of inflammatory bowel disease or cancers of the bowel is frequent vomiting. Eventually affected cats lose weight or stop eating, but this is when the disease is well advanced. If a cat does not respond within a few weeks to a change of diet as mentioned above then we investigate more closely.