Re: Cats eating habits
Hi and welcome!
Cats can be extremely picky eaters. As long as the Whiskas are completely meeting her nutritional needs she should be OK; I suggest not giving her people tuna except as an occasional treat, as it doesn't contain taurine, an essential element for cats health (lack of which for an extended period can result in blindness among other things).
You could try mixing a bit of chicken or beef wet in with her other food, just a wee amount to begin with to see if she'll eat it; don't be too surprised if she manages to eat around it; they're clever that way.
How old is she? Has she been spayed? Have you discussed her diet with your vet?
You might consider posting this on our sister forum, Catsey; many members there are far more knowledgeable about cats nutritional needs than I am!