Redefine the risk: the garden is allowed, the road and the van are not
Proofing advice written for indoor cats misses the point in a rural home. Your cat legitimately roams a large garden, so a delivery does not threaten her with 'outside' — it threatens her with the specific hazards a delivery brings into that territory: a yard gate swung open and forgotten, a lane beyond it, and a large vehicle standing with its doors wide and its engine warm. Your proofing plan should focus on those three hazards rather than trying to keep a country cat behind glass she has never lived behind.
Sequence the delivery around the cat, the gate, and the van
When a delivery is due, call the cat in with the food sound or signal she already knows and settle her in a utility room or kitchen with the door closed until the vehicle has gone. If she will not come in — rural cats have their own schedules — then the gate discipline carries the load: gate shut before the van enters the yard if it needs to, and shut again behind it, with a deliberate check rather than an assumption. Carry sacks and boxes in with the house door closed between trips, and never leave the van's rear doors open and unattended while you are inside, because an exploring cat can be shut inside a load space in seconds.
Check the vehicle before it leaves — every time
Make it a fixed courtesy to walk to the van with the driver and glance into the back and the cab before it pulls away, and look under wheel arches and into the engine bay area on cold days, when a garden cat may have tucked herself against residual warmth. This one habit addresses the rural escape that is hardest to trace: a cat carried miles away in a vehicle, arriving frightened in a strange place with no scent trail home. A delivery note asking drivers to wait for that quick check costs them thirty seconds and can save weeks of searching.
Use the garden's size as a safety feature
A large garden gives you options flat-dwellers lack: a delivery drop box near the gate means most parcels never require the yard or house to open at all, and a fenced inner area around the house gives the cat a roaming space separated from the vehicle turning area. Keep her feeding spot well away from the gate and the parking area, so her daily geography centres on the safest part of the property. If she wears a collar for her roaming life, check its fit and fastening regularly, since a cat pushing through hedges tests a collar far harder than an indoor cat does.
If she is missing after a delivery day
Work outwards in rings: her garden hiding places first, then outbuildings, then the lane in both directions, asking at neighbouring farms and cottages the same day. Tell the delivery company too — if there is any chance she travelled in the van, its route and next stops are urgent information, and firms will usually contact the driver quickly when an animal may be aboard. Leave her bedding and a worn item of your clothing near the house door, since rural cats navigate home by scent over distance. KinsLe's Verified QR ID Pet Profiles put a unique scannable QR on this roaming cat's collar, so a finder on a neighbouring farm can open her profile and contact you on the spot.