MurryB-guess you are just lucky, then.
I know with my nieces and our boys..they like time to plan, to see what they have to look forward too, find excursions they want to take, save some money of their own, etc.
My nieces LOVED the planning. We went shopping for dresses, got pedicures, new shoes, etc. They were all thrilled to be going someone, but there's something to be said for the anticipation and the prepping.
And dont' get me started on the fun our oldest had researching the food we could expect to find. Call me dull I guess, but I would NOT want to be surprised with a vacation on such short notice, in fact I would be upset! LOL...but I am usually the one that has to figure out all the logistics, so I don't want to have to do all that on 24 hours notice....
I did take Mio with me...just put it in my purse to add to the water onboard, all the boys liked that.
Make sure you get all the proper paperwork from her parents in regards to taking her out of the country. That is the most important thing, especially if you have different last names. I would also consider talking to her parents about getting her an ID card. Here in Virginia, we just went to the DMV and got a state issued ID card. She most likely won't need it, but at her age, and since you are not her parents unless she has a passport, it might be smart to have photo ID.