Why don't you point her to the stately home thread, op?
Do you make her buy her own food at home? All her meals? How much does she earn? How much do you take of that for board?
You sound like my mum. First job, first weeks pay 120.00, she took 60.00 board, 10.00 utilities & made me buy any 'special' food I wanted (i.e marmite - which I kept in my room, which pissed her off, as she thought I should share it) then the same every week after that...any wonder we don't talk anymore. And at that time I was paying council tax too. She used to moan that I never went out anywhere (so she & her latest dh could have 'quiet time'), I told her I couldn't afford to!!
I know Disney Florida is expensive but even so... Yes it is, but like you say, even so! I would have chosen a destination that I could have afforded accommodation & flights for ALL my children & just asked the older one to save for their spends.
I have been the excluded child. MY grandparents were allowed to take my sister away, but not me (I was younger, by a year, but even when I was older, they refused) I wasn't allowed on school trips, to do after school activities. Yet my sister got it all.
You have no idea how that feels unless you have lived it. And it had nothing to do with my behaviour, because I was better behaved than her.
I just think, if this is your one special, overseas, family holiday, you will be talking about it for years and years to come, have photos on display, etc, and all she will remember is that she was left out Oh God, I didn't even think of that! All the talking, laughing, memories made....your poor dd, sitting, listening in...

She spends all her money on contact lenses What a shocking waste of money 