This is kind of a tough situation because it's hard to know what's really going on here. But, you basically have three choices:
1. To go and empower her to cope  
2. Don't go
3. Go without her  
I can't make the decision for you but I can say that whatever you decide will have some implications down the road with the way she handles other fears that come up in her lifetime.
 
Option 1: The key to empowering kids to walk through their fears is to validate the feelings but not the content of the fear. So for instance: You could try saying something like, "I don't blame you for missing home. I kind of miss home, too! But whenever I feel a little sad, I think about (insert her favorite Disney ride here). Then, I get so excited that I can't wait to go! I hope you change your mind about how you feel about this vacation so we can all have a good time together." And then let it go. With this approach, you are modeling a way for her to cope without telling her how to do it. Modeling is always more powerful than lecturing.   The more you try to argue her "well thought out points," the more you will validate her fears. Plus, think about all of the attention she is getting from you over this.
 
Here are some points about "Reassurance" taken from my book:
• It is a natural response for adults to reassure a child who is frightened and needy.
• It makes the adult feel better.
• It might seem to help the child feel better temporarily.
• Reassurance can gain immediate compliance.
• Constant reassurance does not build coping skills or resilience.
• It can become an addictive habit.
• It becomes less effective the more it is used.
• Can create more worry and concern in the child.
• Use truthful reassurance sparingly and only if it doesn't lead to more worried questions.
• Use empathy, encouragement, choices, and descriptive phrases instead.
 
So spend alot more time with her on planning fun things to do and going to the Disney website to look at the maps and watch the Disney resort DVD together than you do "discussing and arguing" her fears.
 
So in summary: acknowledge the fear but don't dwell on it. Empower her to cope. Dwell in the fun stuff. Give her the "can-do" message, ("Lots of kids have fears about things but I think you're one of those especially brave kids who just keep on going despite their fears.")
 
Option 2: I don't recommend this because it just isn't good for a child to know that he or she can make such big choices that affect the whole family. But if you think your trip will be totally miserable (you know your child) then maybe this is something you should consider. And if you decide not to go to Disney, I would suggest that you make a point to go away, just the two of you, for a couple of days at least. Her fear should not ruin your special time together. Vacations are also for the parents- not just the kids. :-)
 
Option3: One option is to go on the vacation without her if you have family nearby to take care of her for a few days. But make sure you discuss this with her and give her the choice.
 
Happy Parenting!
Parent Coach Lisa
 
These ideas are from the award-winning Love and Logic book "Parenting Children with Health Issues." Love and Logic is a well-known parenting program that has been used in schools and homes around the world for over 30 years. www.loveandlogic.com
 
Parent Coach Lisa is a Love and Logic author, public speaker and parent coach. She is the co-author (with Foster Cline MD) of "Parenting Children with Health Issues." www.ParentingChildrenWithHealthIssues.com