Congratulations to Princess Alexia! She looks effortlessly beautiful and love how the photo just looks like a very normal family in their daughter's graduation. Since the exam result won't be communicated until early July, I wonder if a photo of her hoisting her school bag along with the Dutch flag will be released just like Amalia did, or it will be just short press release that she got her diploma since the timing would be irrelevant.
Anyway, regarding to Ariane's school choice -- when applying for UWC, applicants should've applied for the movement itself, not for a specific school. Therefore, choosing which school to attend is not an option. However, when applying, they are allowed to list school preferences. It is up to the selection committee and the school itself whether or not to accept them based on slots available for each country (in Ariane's case, The Netherlands), scholarships availability (this certainly won't be her case), and if the school is a good fit for them (each UWC is different). For Ariane whom her parents could pay the full fee for every UWC school, I imagine it should be easier for her to get into her first choice though. If it is, her admission to the school should be supported by the committee's opinion that the school is indeed a good fit for her in one way or another. Whether she truly has artistic talents, has the passion of integrating herself into a whole culture in her day to day life, or simply a young woman who loves interactions (since the school is an open campus).
Along with the fact that she already speaks Spanish (and don't forget her current school also teaches Latin), UWC Adriatic requires its students to learn Italian, even if it means it had to be their 7th subject (instead of the usual 6) and admits a handful of Italians each year - so she should be good.
Cost of attendance would be around 46.000 Euros per year - about half of Alexia's school, the Atlantic College.