A practice visit does the heavy lifting
The single most useful preparation is a rehearsal. Arrange for your puppy to spend a few hours with the sitter in the sitter's home before the wedding, with you dropping her off, leaving, and collecting her later, so she learns three things in advance: the house is safe, the sitter is kind, and you always come back. If the wedding stay includes an overnight, make the rehearsal an overnight too if you possibly can, because night-time in a strange house is the part puppies find hardest and it should not debut on a day when you are unreachable at an event.
During the practice visit, let the sitter follow the real routine, a meal, a toilet trip, a play session, and a nap in the bed she will use on the day. Any problem, such as refusing food, barking at the sitter's own dog, or struggling with their stairs, surfaces while there is still time to adjust the plan.
Packing her home comforts and her exact routine
Send the food she already eats, portioned into labelled bags or tubs for each meal, because a wedding weekend is the worst possible time for a diet change to upset a puppy's stomach. Add her own bedding unwashed, so it smells of home, a safe chew she knows, and one item of your worn clothing for her bed. If she uses a crate at home, send the crate rather than expecting her to settle in a borrowed one with a different smell and door sound.
Write down her day in the order it happens: wake time, toilet routine and cue word, meal times and amounts, walk length she is used to, the cues she reliably knows, what settles her in the evening, and your vet's number plus a contact who can collect her in an emergency. Note anything the sitter should not do, such as off-lead play in an unfenced garden or meeting unfamiliar dogs on a walk, in plain terms rather than assuming it is obvious.
On the day itself
Time the drop-off so she arrives settled rather than straight from a frantic car ride, and keep your farewell short, bright, and boring. Long emotional goodbyes teach a puppy that departures are significant events worth worrying about. Hand over the lead, confirm the collection time, and leave promptly; most puppies turn to investigate the sitter's house within a minute of the door closing.
Ask the sitter to keep the day deliberately ordinary, her normal walks at her normal times, familiar games, and plenty of rest, rather than a programme of exciting visitors and new places. A tired, overstimulated puppy in a strange house by evening is far more likely to cry, toilet indoors, or refuse to settle than one who has had a quiet, predictable day. A photo update or two during the wedding is reasonable to agree in advance, but constant checking helps neither you nor the sitter.
After she comes home
Expect her to sleep heavily for a day and possibly to be clingier than usual or, conversely, briefly aloof; both are normal after a first stay and settle within a couple of days. Return straight to her home routine rather than compensating with extra excitement, and note what the sitter reports, what she ate, how she slept, any worries, while it is fresh, so the next stay starts from knowledge rather than guesswork.
Putting her feeding times, toilet cues, settling routine, and emergency contacts into KinsLe as a Care Pass means the sitter opens one clear, temporary set of instructions on the day instead of hunting through messages, and you enjoy the wedding knowing nothing important lives only in your head.