I'm gonna have to disagree with DJA - there is a lot of motion on the Grand compared to other ships! It's known as a "rough rider" among the newer ships. Does this mean you'll really feel the movement - no, especially if you are mid-ship and the weather is calm. The winds play a big part in the Grand's movement. High winds = more movement.
We've had a very aft cabin (VS on the Emerald Deck) in really bad weather. The ride was terrible, the noise was incredibly loud (creaking, moaning, etc) and I'd never book an aft cabin on the Grand again.
We also had D701 which is somewhat aft during the same exact week as the other time on the Grand with totally different weather. We hardly felt a thing! It was quiet, smooth and absolutely beautiful.
My sister had a mid-ship balcony cabin on the Aloha Deck and really felt the movement during high winds. Otherwise, it was fine.
Mom had an Emerald Deck mid-ship cabin and never felt much movement at all during the bad weather we had.
SOOOOO, it's a crap-shoot. Try to at least get a mid-ship inside cabin and most of all, go prepared and you (and she) will be just fine.
And yes, there's still a chance you'll get upgraded. I've had friends that had a cabin assignment many times and have been upgraded to the PH suite once, and twice to a balcony cabin.
