I'm wondering whether Holly may not have a food intolerance of some kind.
Common no-nos are beef, wheat and dairy - a friend's Burmese is intolerant to all three.
The cheaper dried foods e.g. Whiskas, Go-Cat, supermarket brand have a high proportion of wheat in them as well as beef and they can be the cause of digestive issues. One of my cats leaks from both ends if he eats Go-Cat. Also, he has similar problems with Whiskas wet food (cans / pouches).
What I suggest you do is try feeding her some plain boiled chicken and rice for a few days and see if that helps with the "poopage" problems. Firstly, it should settle her tum as it's light and bland and secondly, if it does firm up her poos, you can then slowly add other foods to her diet and keep an eye on things. If something then gives her a runny bum, then you'll have a fair idea that it doesn't agree with her.
If you feed her mainly dry, then perhaps look for foods that have no wheat or beef e.g. Purina One, Purina One Natural, James Wellbeloved, Royal Canin or Orijen. If in doubt, check the label. Also, Royal Canin do a food for sensitive tums, so may well be worth a look.