A sitter can keep her feeding, her litter trays, and her company exactly right and still damage one thing without meaning to: her weight series. One well-meant weighing done a different way enters the list as if it belonged there, and every reading after it inherits a bend in the trend that never really happened.
Teach the Method, or Agree to Skip Weighing Entirely
Your list is a running, dated record of her weights, always weighed on identical scales under identical conditions, so anyone can see at a glance which way the trend runs. Before you leave, perform one weighing with the sitter watching: the same scales, the same hard floor, the same point in her day, the same carrier method if she is weighed in her carrier. Then let the sitter talk the steps back to you, because watching once is not the same as being able to repeat it alone.
If the sitter doubts the method, or she is unsettled by being handled for it by a newer person, agree plainly that the sitter will not weigh her at all. That is the right outcome, not a failure: the point of the series is method consistency, and a gap in the dates harms nothing while an off-method entry harms the whole list. Write whichever you agreed at the head of the sitter's notes.
Settle the Sitting Terms and the Daily Notes
If the sitter is paid, get the agreed terms confirmed in writing before the stay, covering the dates, the pay, the visits each day, and what happens if you return late. Ask the sitter to keep a simple daily note of how she ate and drank, because appetite notes explain a later weight entry far better than the entry explains itself.
Tell the sitter where her scales live and where the list lives, and ask for any entry to be written with its date on the day it is taken, never reconstructed at the end of the stay. If the sitter notices she feels lighter when picked up, or her collar sits looser, that belongs in the daily notes as an observation to discuss with you and, if it persists, with her vet, rather than as a reason to improvise a weighing.
Do a full practice run before the stay begins, ideally on an ordinary evening when nothing else is being handed over: the sitter weighs her start to finish while you watch silently, then reads the entry back from the list. That single rehearsal surfaces every misunderstanding while you are still there to correct it, from a scale placed on a rug to an entry written without its date. If she dislikes being weighed by the sitter even in rehearsal, take that as the answer and agree to the no-weighing option on the spot, in writing, so nobody relitigates it mid-stay out of conscientiousness.
Protect the Series When You Return
Weigh her yourself, the usual way, soon after you are home, and read the sitter-period entries, if any, against that figure and against the last entry before the stay. If a sitter entry was taken a different way despite the agreement, do not delete it in embarrassment; mark it clearly as off-method beside the entry, so the series stays honest and no future reader trusts it as part of the trend.
A weight worry that survives the return weighing is a conversation for her vet, armed with the list, not a goal figure set at the kitchen table. Her method-guarded list stays inside Pet Passport with its method written plainly, and KinsLe keeps that list trustworthy across every sitter stay to come.