The child has not thrown a temper tantrum. She has simply said she does not want to go to Disney again and would prefer a cruise. She is not sulking but she is not enthusiastic.
AN 8 YO probably would not have the ability to articulate that she wants to vacation at home with her family. An adult would. Her parents have included her opinion when making their vacation decisions. She enjoyed the cruise they took her on. The child may have see a
Disney Cruise as the best of both worlds and had no idea that she was asking her parents to spend about 3 grand more.
Instead of telling her how lucky she is and that others get less perhaps the parents can use this as an opportunity to teach her how they come to the decisions they do. When the child has made a decision in the past she probably was given a list of destinations. Her parents already narrowed her choices down so that they fit into the time-frame and budget. It seems to me that this is a perfect time to explain that to her, show her what goes into paying for a Disney Cruise, the time involved as well as the length of time it takes to plan it in order to make sure that the family gets the most out of that vacation.
It really is not fair to make a child feel guilty because circumstances have given the child more vacation opportunities than some other kids have had. It is a good time to help her to learn about priorities and how to manage them.