Tinker,my 14 year old cat,has gone off whiskers & felix,for 2 weeks eating 'hard'food only,so I've tries gourmet,£1 extra, which she's eating like a starved wolf,typical cat eh?!
i'd get her to the vet for a checkup, murph went super fussy on food, turned out it was thyroid problems which is being controlled by drugs now shes the same sort of age, 14/15 not 100 sure exactly.
and having to give her a pill every day is just super fun
cat's are picky,being higher forms of life(gods),but has always eaten felix or whiskers,but as you say,wise to check.she has a bionic pelvice after a hit & run as a kitten,been lucky otherwise!