Yes, the sardines you currently have are no good in this context.
Many cats have trouble if they go too long without food, eat too much at one meal, eat too fast, swallow pieces too large, or go through a change in diet too fast. Kidney and other organs are also a frequent cause of nausea.
Here are my solutions to each problem (and yes, unfortunately, I've hit all those listed):
Too long without food and eating too much at one time: My cats eat a minimum of three times a day. Right after my morning shower (so they associate breakfast with my shower and not my waking up), right after I get home from work, and the very last minute before I go to bed (and I seldom sleep more than eight hours a night).
Eating too fast: I cut this cat's pieces really large so she HAS to slow down to eat.
Swallowing pieces that are too large: Until she became more proficient at scissoring off smaller pieces on her own, I cut Rachel's meat chunks smaller than her housemates'. Today, all the cats are experienced raw food eaters and if one horks up his/her meal because he/she didn't cut it down enough, it's almost 100% of the time while they're still in the dinner cages, and they just re-chew and re-swallow the food.
Diet changes: I feed a large variety of foods so the cats' systems can handle changes more comfortably. I also made all changes at the cats' pace.
Organ meals: Initially, I tried to feed liver once a week and kidney once a week, but this was too much at one time for several of my cats, so I divided that in half and now feed liver (and chicken gizzards) twice a week and kidney (and chicken breast) twice a week. Ralph still had issues so I switched to a poultry liver (rotating between turkey and chicken) instead of beef liver, which solved that problem. His kidney meals, however, have to be chopped fine, mixed well with the chicken breast and sprinkled liberally with freeze-dried 100% chicken meat treats.
Some cats also have problems when the food is too cold (this one, I haven't had): The easiest fix here is to put the food in a plastic baggie and let it float in warm (not hot) water for a few minutes.
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Hopefully, one or some of these solutions will help Krystal, too, SKT.