I think Eustacia was among my earliest reads. I definitely remember particularly wanting to read it, because I thought it was a lovely name.
But yes, reading it now it's actually the only Tyrol book I don't really like, because the treatment of Eustacia is so unkind. I know EBD likes conformity (understatement), but that sort of meanness towards the girl who doesn't fit in seems so much more Blytonesque. :( (I do get that it's of its time; perhaps this is more of a mark of how some of EBD's philosophy actually hasn't dated as much as her contemporaries?)
I think I'm repeating myself, apologies, but I think Eustacia is quite an interesting one now because the staff seem to screw up quite a lot, which isn't very CS! Mlle is conspicuously weak in her leadership, IMO (I think it's clear from this book that Hilda is the future); Con Stewart, who I rather love, manages to inflame the situation quite badly. Where is Madge, is she Busy? I can't remember her being much use either, in contrast with how she helps Juliet in earlier books. I do however like the bit when Stacie apologies to Bill, years and years later in Reunion - probably just because it's a trip down memory lane, and it's also nice to see that laid to rest and having someone finally tell her there was no need to apologise.
It's an interesting question, re EBD and Brexit. I think her passion for Europe would sway her as well as the logistic difficulties it would pose for a school run on British lines in Austria or Switzerland, and I also think she's never too fond of English peasants, preferring the simpler, more pious continental version! I think she'd have definitely had opinions on it, though.