01Start with the obvious, then go deeper
The box itself is often the culprit. Cats are fastidious, and a tray that a human finds "fine" may be genuinely offensive to a nose roughly fourteen times more sensitive. Scoop at least once a day, fully empty and scrub the box with mild soap weekly. If you have multiple cats, the rule of thumb is one box per cat plus one spare — crowding at the tray creates avoidance fast.
Next, look at the litter. Most cats prefer a fine, unscented clumping clay; heavily perfumed litters mask odour for us and overwhelm them. If you've recently switched brands, switch back and transition slowly. Depth matters too — about five centimetres suits most cats, who like to dig and cover properly.
Location is the third lever. Boxes tucked next to loud appliances, in draughty corners, or right beside the food bowl get quietly boycotted. Cats want privacy but not a trek — somewhere calm, consistently accessible, and never adjacent to where they eat. In a multi-storey home, one box per floor is worth it.
Once the practical basics are right, think stress. A new pet, a house move, building work, or even a change in your schedule can push a cat into eliminating elsewhere. Look for other signals — hiding, over-grooming, reduced appetite — and if you're seeing them, read up on understanding cat behaviour to get a fuller picture of what she's communicating. Feliway-type pheromone diffusers have genuine evidence behind them for stress-related house-soiling and are worth trying before anything more drastic.
If you've worked through all of the above and the problem persists, see your vet — sooner rather than later. Urinary tract infections, bladder stones, arthritis (which makes climbing into a high-sided box painful), and kidney disease can all show up first as litter box avoidance. This is the category where waiting costs you.
A quick diagnostic order: box hygiene → litter type → location → stress → vet. Most cats resolve at step one or two. The ones who don't are usually telling you something medically real, and they deserve to be heard.