How come you put her/them on a dry food only diet in the first place, Chris? To lower the BP?
Our first cat, Mogs, lived to 17. Properly fast, active cat. He ate anything 'n' everything..... curry, Bombay duck, jam sandwiches lol He then was off his food for a few days and died pretty suddenly.
Alf also lived to 17. He was the exact opposite of Mogs.... long haired fat barsteward
but ironically didn't eat much above what he got for dinner. And didn't like anything other than cat food (apart from ham slices).
Originally through ignorance tbh. Wet food stinks, and costs more. So dry food fixed both those plus the alleged benefit of keeping plaq off their teeth.
Buyer beware as they say. As a lot of the dry food is full of sugar. Good for teeth aye?

There was an element of addiction to the sugar as well, ESP in IAms.