hi alison, i just came back from a princess cruise a few weeks ago (caribbean princess)
and it was wonderful.
i suggest when you get to the ship get someone immediatly to help you and you will have someone with you until you arrive in your stateroom! also you will be first on the ship!
no stress, let someone else do the work, they will wheel your sister on with no problems
The dining room you will have a choice whether to stay in you chair or get out of it and they will store your chair at the side!
Have you a handicapped room?
I am in Canada so the travelling would be shorter.
As i think of others things i will let you know. Hester.