You might ask the vet whether it would be beneficial to try giving lysine--if the sneezes are caused by a feline herpes infection, it could help. It sounds like she may be congested, and that can often cause a cat to eat less, either because it is hard to eat and breath and the same time or because they can't smell the food. You can try gently heating the food for a few seconds in the microwave to enhance the aroma, and you may want to try putting her in a steamy room or using a humidifier to help clear her nose. Actually, saline nose drops might help too.