Ahoy, Donna!
While I typically tend to try and book a stateroom that is midship, my husband and I spent an amazing 10 nights aboard the beautiful Disney Magic last fall in stateroom 7621. It is near the aft of the ship, and we slept like babies. I do not find there to be as much vibration on the Disney Magic as I do on the Disney Dream in the aft staterooms, maybe due to the difference in size of the ships.
If you think you will be sick while onboard, it is definitely a good idea to plan for the worst. I have heard great things about the sea bands, which can be purchased at your local pharmacy or onboard.
Your daughter is the perfect age to enjoy a Disney Cruise Line vacation! My youngest daughter was 11 on the Dream this summer, and spent most of her time in
Edge, the tween club. She made so many great friends, and stayed out to all hours with them.
I hope this helps with your cruise planning! Please visit us again here at the Disney Parks Moms Panel with more questions before you set sail!
Happy Cruising, Tracy V.