The very best thing you can give your cat for hairballs is canned pumpkin. (Not pumpkin pie filling). Mix 2 spoons in with some canned cat food every single day. This will prevent her from getting constipated and it will also help hairballs pass through the system and prevent the vomiting that is associated with them. If you use it regularly, you probably will not see any more (or very few) hairballs from your cat in the future.
If your cat has a tendency to get frequent hairballs, you can also help by combing or brushing daily to remove dead hair which is what causes the hairballs in the first place. Even if your cat is a short hair, they shed an amazing amount of hair every week, and removing it for them helps greatly.
You really don't want to give cod liver oil except as a last resort if your cat is unable to get a hairball up at all. It will not only get the hairball up (or out), it will probably give your cat diarrhea also.
Please let me know if I can help further.