regular tuna can deplete viatimins in kitty ... best thing to do is give kitty tuna flavored cat food as the viatmin issues are taken care of via added vitamins... what brands are you feeding if I can ask??
If you don't offer her tuna she won't have a choice and will get hungry and eat what you offer her. I know it sounds harsh but as long as you offer her the tuna she is going to eat that over everything else. Try tuna flavored pouches or cans.