I'm going to give my wife a vacation ultimatum
Why do you think that you need to do this? It sounds like something happened
That's my last resort. I still love her
If you love her still I would reconsider giving her an ultimatum. I think that this can anger people and you want to be able to enjoy your vacation. That means you should avoid the fight with her.
She never spends time with me, I'm going to refuse to stay in the same room with her.
How will staying in separate rooms on a vacation help the relationship? You probably want to be in the same room and just enjoy everything the vacation offers. I think getting some intimacy in the relationship will help a lot.