This is flat out unacceptable. I’m not a fan of ultimatums but this is a situation that will either make or break the relationship in my eyes. I probably wouldn’t explicitly say that if she goes it will be over between us, because it shouldn’t require a step like that for her to see how disrespectful and selfish she is being. And if it does require that step, then she’s just not a good partner. My advice, explain how messed up her plan is and how much this hurts your feelings and has you rethinking the relationship. If she still goes, II’d 100% end the relationship and either enjoy the rest of the trip solo or head back early without her.