The cat may have hairballs that cause the cat to throw up. Get a hairball remedy, if the vomiting continues, you need to schedule an appt with the vet.
Your cat may have developed an allergy to the food or maybe some sort of digestive problem; in either case, call the vet; the cat probably needs to be hydrated at the very least and maybe a little something to help the digestive process along. Good Luck!
Change the cat's food - this is not good for the cat and the cat may be creating a habit in which the cat simply does not keep food down.
It could be that your cat doesn't like the food you are giving her. Try different foods. If that doesn't work then just take her to the vet.