I used to use petromalt to prevent hairballs. That includes the petroleum. And as I recall, it comes in a salmon flavor. Sounds like she has hairball issues:

Symptoms of hairballs include constipation, straining during a bowel movement, dry cough, and vomiting after meals. The use of Petromalt and regular brushing of cat's coat will generally eliminate these problems.
- http://www.petco.com/product/2700/Se...ll-Relief.aspx

It comes in a paste and as a treat:
http://www.thatpetplace.com/pet/prod...=10#resultBody

You can also use melted butter:
http://animals.howstuffworks.com/pet...r-cats-ga7.htm

Oh, I say "used to use" because since I switched to high quality food, (Chicken Soup for the Cat Lover's Soul kibble) and then to grain free, my cats no longer have hair ball issues.