When Genever hacks up a hairball, I give her
Laxatone for a few days. Luckily she loves the malt flavor and licks it off my finger like a treat. If your cat doesn't like it, then put it on her paw and she'll lick it off to get cleaned up.

Otherwise, you could try hairball treats, I think they have mineral oil or something like that in them to get things moving along... You can find either at Petco/Petsmart or online or probably even at the vet. I've bought Laxatone from my vet before and it actually wasn't much more than what I'd paid at Petco. Good luck!