Sharing a dog's costs with a co-owner works smoothly right up until someone needs a specific receipt — for an insurance claim, a question about what a procedure cost last time, or the end-of-month settling up — and it exists only as a crumpled paper in the other person's car. Receipts for shared expenses need a shared system: one place, one order, and entries complete enough that either owner can act on them without a phone call to translate.
One shared record both owners actually maintain
Agree on a single home for receipts that you both can add to from your phones: a shared folder for photographs of paper receipts plus a simple running list. The list is where the system lives. Each entry carries what the receipt was for, the total, which of you paid, and the split you agreed for that item, because splits are rarely uniform — routine food may be shared evenly while a discretionary purchase belongs to whoever chose it. Photograph paper receipts the day they are issued, in flat light with the whole slip visible; thermal paper fades, and a faded total helps nobody during a claim. If a receipt is emailed, move it into the shared folder the same day rather than leaving it in one person's inbox where the other cannot reach it.
Sorting by the dog's life, not by the payer
File by category — veterinary care, food and supplies, training, grooming, boarding and daycare — instead of by who paid or by the shop's name. Categories answer the questions you actually ask later: what did her dental work cost, how much is food running each month, what did boarding come to across the year. Within veterinary care, keep procedure receipts beside the matching treatment notes so a claim or a follow-up question can be answered from one place. One-off large costs deserve a short note attached at the time — what was decided and why — because six months later neither of you will remember the reasoning, and co-ownership runs on remembered agreements far less well than on written ones. If your household tracks who owes what on a notebook page or a whiteboard, photograph that page at each settling-up and file the photo with the month it belongs to, so the running list is not the only witness.
Settling up without the archaeology
Set a regular rhythm, such as a short review at the same point each month, where you both scan the running list, confirm the splits, and settle the difference. Short and frequent beats an annual excavation through two phones and a shoebox. Keep receipts that support insurance claims, warranties, or anything tax-related in their own clearly marked section and do not thin them out during tidy-ups; routine supply receipts can be reviewed and pruned once the settling period they belong to is closed and agreed. If you disagree about an item, the entry's note from the day of purchase — not memory — should settle it, which is the whole reason the notes exist. When the relatives you choose can open her profile in KinsLe Family Sharing, the receipt record rests on a dog they know first-hand rather than in two private piles.