The second they introduced the cousin in the letter and that she mentioned she has a male cousin, I've already thought of it... Hopefully she gets restless again like the time she thought someone was going to confess to Elsa when Elsa received what looks to be a love letter and destroys that date
Some part of me almost expects Yvonne to ask Elsa to send this letter for her please, and it "mysteriously never arrives at it's destination" (with a side of, "Oh no, Elsa, you have some soot on your skirt!").
But if we accept both that the author will keep her promises AND the Evie-like Existence will appear, I kind of hope he takes one look at the situation and is like "Okay, Elsa, we need to make a plan because otherwise you're never gonna get the girl."