Low enough for a walk-in step
The entry of a litter tray for an older Domestic Shorthair should be low enough that she walks in with an ordinary step, keeping her back level, rather than hopping, scrambling, or lifting one hind leg high over the rim. There is no single height that suits every senior cat, because leg length, joint stiffness, and balance differ. The right test is her movement: a smooth, unhurried step in and out, with no pause at the threshold, means the entry is low enough for her today.
Watch her from the side as she enters. An older Domestic Shorthair who plants her front paws inside, then hesitates before bringing her hind legs over, is telling you the rim still asks too much of her hips. A cat who drags a back foot across the edge, catches a claw, or lands heavily inside needs a lower entry or a shallow ramp up to a cut-down side, even if she eventually gets in.
Cut one side down and keep the rest high
A practical tray for an older Domestic Shorthair has one lowered entry side and three higher sides. The high sides still contain kicked litter and give privacy, while the low side becomes her doorway. Many owners cut an entry into a sturdy storage-style box or choose a senior tray made with a dropped front. Smooth any cut edge fully, because rough plastic at belly height will catch fur and skin on a cat who steps slowly and close to the edge.
Keep litter shallower near that entry so she does not step from a low rim straight into a deep, shifting pile. A firmer footing just inside the doorway helps an older Domestic Shorthair turn and dig without her hind feet sliding. Place a low-pile washable mat outside the entry to catch tracked litter, and make sure the mat itself does not bunch into a new trip edge at the exact point she steps down.
Read the signs the height is wrong
Accidents beside the tray are information for an older Domestic Shorthair, not misbehaviour. Waste just outside the entry often means she got partway in and gave up, or could enter but could not posture comfortably once inside. Perching with two paws on the rim points to a tray that is either too high to enter or too small to turn in. Stepping in and straight out without digging can mean the entry hurt on the way in and she is hurrying the whole visit.
Change one thing at a time and give her several days with the new setup. Lowering the entry, enlarging the tray, and moving its location in a single weekend makes it impossible to tell which change helped an older Domestic Shorthair, and too much novelty can put a senior cat off a tray she previously accepted. If she uses a second tray elsewhere in the house, match its entry height too, so she is not choosing between a comfortable tray far away and a painful one nearby.
When a low entry is not the whole answer
Contact a veterinarian if an older Domestic Shorthair still misses the tray after the entry is genuinely low, strains or cries while passing waste or urine, produces much smaller or larger amounts than usual, or stops eating and hides. Those signs in a senior cat can point to problems that no tray design can fix, and they deserve a check rather than another box. Bring notes on when the misses happen, whether she enters and leaves quickly, and what you changed, because that sequence helps the veterinarian judge whether the barrier was access, comfort, or something medical.
Once you find the entry she uses confidently, record the tray type, which side is lowered, and where it sits in KinsLe Pet Passport, so that setup travels with her records to anyone caring for her.