Go on your holiday! Your sister doesn’t own the destination. Don’t let your sister’s selfishness spoil this lovely holiday for you.

You know what? I have a sibling who is well travelled and has been to most of the places I want to go to. I haven’t been to most of them yet, but they’re not ruined or any less lovely because my sibling has been there already. Honestly it’s irrelevant. If I get a chance to go to those places, a) it will be exciting and special because I am there, me, in real time. And b) millions of people have been to these places before my sibling got there, and millions will go there subsequently.

Whole countries and tourist destinations are not all about your sister. They’re popular tourist destinations because hundreds of thousands or even millions of people love them.

Ignore the tantrums. NTA.