One File, Agreed by Both Homes
Joint care fails on records when each home keeps its own version and the versions quietly diverge: one of you holds the vaccination card, the other books the booster, and neither file is complete. The remedy is a single shared record that both of you treat as the only record. It holds the microchip and vet details, vaccination history, a dated log of vet visits and costs, and the running care notes. If it is not in the shared file, it did not happen, which sounds strict until the first disagreement about when a symptom started.
Settle the Registered-Keeper Questions in Writing
Some things cannot be shared equally on paper. One name will sit on the microchip registration and usually one account at the vet, so agree whose, and record the agreement where both of you can find it. Write down the handover schedule, how routine costs split, who pays for food and litter at each home, and, most importantly, who can authorise emergency treatment if the other is unreachable. Vets in an emergency need one clear decision-maker, and deciding that calmly now protects the cat from a phone argument later.
Keep the written arrangement short and factual. It is a care document, not a settlement, and it works best when either of you could hand it to a vet, cattery, or new partner without embarrassment.
Log Handovers Like a Relay
Each handover deserves a brief dated note: when she last ate, litter tray observations, anything unusual such as a missed meal, a limp, or being quieter than normal, and any medication given in general terms. Health patterns hide between houses, because three days of reduced appetite split across two homes can look like nothing in either one. A continuous note thread exposes the pattern, and it also protects both of you from suspicion when something is genuinely wrong, since the observations are timestamped as they were made.
When the Arrangement Changes
Joint care arrangements rarely stay frozen. Jobs change, one of you moves further away, a new pet arrives at one home, or the cat herself becomes elderly and the travel between houses that suited a young cat starts to cost her. Build a review habit into the shared record: every few months, read the agreement together and adjust the rota, the cost split, or even where she lives most of the time, recording the change with a date so the file always shows which version was live when. If relations between you become strained, the dated record you built in calmer times is what keeps her care steady and her history unquestioned, which is exactly why it was worth keeping impersonally and completely from the start.
Keep the Cat's Experience Consistent
Use the shared notes to align the basics across homes: same food, same feeding rhythm, same house rules about outdoor access, so her body and behaviour are not whipsawed by the rota. Note her preferences and stress signs where a new partner or visiting family member at either home can read them too. Her profile itself can be opened by the relatives you select, once you give them access through KinsLe Family Sharing.