There's no way it will be an order to reject Elsa. It's almost definitely an order to [blind prediction] give her a kiss, or something similar. The last couple of orders were more naughty than harmful after all.
I don't think you need spoiler tags for guesses but eh.
Since this is a side chapter insert to the original story, it's definitely not going to be anything of major consequence, so I'm going with "It says to cut her with the knife" as somebody else suggested, and she gets around it by doing a finger-prick blood-sister oath or something.