I am sorry your baby is having trouble.
Check inside her mouth for a bad tooth or stuck item.
If she eats only dry food that may be the culprit. Please read:
Cod liver oil is not good for cats. Instead give her tuna, salmon or sardine oil @ one tsp a day.
Cats are obligate carnivores meant to eat meat.
Add some canned food for her. It prevents hairballs:
Here is a natural product:
Cats are attracted to smelly foods - the stronger the better. If she wants tuna, give it to her You can also try fancy feast, clam juice or baby food.
Human baby food in meat flavours (check that there are no onions or garlic in the ingredients) and mix that with warm water and offer that, or syringe it in little bits into your cat's mouth. Beech Nut makes a line of baby food that has nothing but meat (beef, chicken, turkey or veal) in it. Here's a link: http://www.beechnut.com/Our%20Baby%20Food/Results.asp If you cannot find this, you could find another meat baby food - just read the label carefully to be sure there are no onions, onion powder, garlic, or garlic powder in it.
If the gagging continues her teeth should be checked.
Please let me know how she is doing. I will always be here for you.
I hope she feels better very soon.
Sincerest best wishes,