There should be only one shuttle bus area for RCI. I suggest planning on meeting up there.
Tell the shuttle driver you are meeting your sister and maybe they can take her name down t ohelp match you up. You will be going to retreive your luggage anyway. You should inform the shuttle bus "crew" that you are there so that they know you are needing transport. If your sister's flight is late or something, you can be told when the last shuttle leaves.... that is what I would do anyway.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013