I have a 9 year old who regularly says that things her 6 yr old brother likes to do is 'babyish'. She does it to try to get her own way, so, tv show is babyish, so she can get to watch an older child related show, or get to go to a park that is where she wants to go. But, actually, she still loves those 'babyish' shows and watches them avidly with DS when they are on, and loves those places.
9 is a perfect age for disneyland imo. She doesn't want you to know quite how much she would enjoy it for some reason. wants to appear grown up, doesn't think you are actually going, so has no reason to actually show a real interest, just using it as a way to show you she is not a baby any more.
But, actually, regardless of her moods, her stroppiness, her denial of enjoyment of this kind of thing, she 6does not mean it^. 9 year olds were learning to manipulate with words, with behaviour, to get reactions, to test how you feel about them, to test their security. Your job is to remain there for her during these tests, to show her that you are, and always will be there, and that she is important and loved. If you exclude her from an enormous family holiday because of her 'poor' behaviour, you are showing her that actually, her fears of not being important, not being loved, not being there for her, are real. You will in effect destroy your relationship with her, and potentially between her and her siblings.
I am absolutely amazed, and sad for your DD that you would even contemplate going away without her, and thinking that you would have a better time without her there. If I went on a holiday like that without my DD, no matter how bad her behaviour, I just couldn't enjoy it, as I would feel the family was not complete, I would constantly be reminded of things she might enjoy, was she sad without us. How could you enjoy it without her there? Maybe you need to think about a holiday that everyone would enjoy, including your DD.