Bring everything down to ground level for a large, stiff rabbit
Ground-level everything is the adjustment that changes daily life most for an elderly Californian rabbit, because this is one of the largest rabbit breeds and every hop up or down moves serious weight through stiff joints. Move hay, water, and her litter tray onto the floor she lives on, and retire ramps, hutches with raised levels, and platforms she once used without thinking.
Keep the distances short as well. An elderly Californian should be able to reach hay, water, litter, and her resting mat within a few unhurried steps of each other, so that a stiff morning never means choosing between comfort and a long walk to breakfast.
A low-entry litter tray she can step into, not climb into
A low-entry litter tray matters greatly for an elderly Californian, whose aging hips may no longer lift her cleanly over a high tray side. Cut one side down or choose a tray with a low entrance, line it with soft hay over the litter, and make it wide enough for a large rabbit to turn around in without squeezing.
Add a second tray at the other end of her area if her space is long. Older rabbits often leave toileting later than they should when the only tray is a journey away, and a nearby second option prevents both accidents and the discomfort of holding on.
Non-slip routes between the places she uses
Non-slip runners along her main routes protect an elderly Californian every hour, not just at exercise time. Trace the paths she actually walks — resting mat to litter tray, tray to hay, hay to water — and lay carpet runners or mats over hard flooring on exactly those lines, because a heavy rabbit who slips lands hard.
Check that rugs stay flat and do not bunch. A Californian's weight can ruck a thin rug into a trip hazard, so use backed runners or fix edges down, and re-check after every clean.
A resting place built for a heavy senior body
A wide, padded resting area supports an elderly Californian's body properly, spreading her considerable weight so elbows, hocks, and hips are not pressing on hard floor through long senior sleeps. A thick mat or folded blankets in her favourite corner, with a low hide she can walk into rather than hop into, gives her rest that restores instead of stiffening.
Keep the resting corner draught-free but not hot, and in the same place every day. Senior rabbits navigate partly by habit, and a Californian who knows exactly where rest is will use it before she is exhausted rather than after.
Food, water, and daily checks within the same small world
Accessible food and water complete an elderly Californian's adjusted home: hay in at least two ground-level spots so one empty rack never means a hungry wait, and a heavy bowl as well as a bottle, since a stiff neck may find one easier than the other on a given day.
Do a brief daily once-over as you refresh things — eating normally, droppings normal, moving as expected for her. Recording the home changes you made and how she responded in KinsLe's Pet Passport keeps her senior setup documented, so a vet or a covering family member can see exactly how her world is arranged and why.