Thanks for the help. In the end I got some skinless, boneless haddock fillet and chopped it up (actually with a pair of scissors - worked well!) then gave it to her raw just to see. She LOVED it. Wolfed it down like I've not seen her do with packet food. And no more diarrhoea. Yay!

Do cats get all the nutrients they need by eating raw?

In fact, I'm sure I can find that answer on the forums!