It's the problem with EBD's total obsession with Joey in the later series -she ends up sidelining or actually banishing beloved familiar characters to concentrate on Joey - even in books like Reunion, which were clearly intended for adult fans to reencounter some of the original school (but which is weirdly disappointing, as, say, Juliet, who does attend, doesn't get any narrative attention at all..) And Madge gets sent offscreen to Canada and Australia.
And yes, not only is the famously delicate Robin, Joey's adored baby sister, packed off to be a nun in Canada, but when she subsequently spends a year at a French convent, none of the Maynards go and see her from Switzerland, even once.
Elisaveta is widowed after the war, and continues to be regarded as princess in exile while Belsornia is in Soviet hands, but her father gies too ranching in Australia, and her children don't use titles or expect to return. Her life is rather sad, but EBD clearly likes the idea of the exiled princess fallen on hard times, because there's an unintentionally hilarious bit during the war where Elisaveta, her children and her servant all escape to Wales, but for some reason don't contact Joey or the CS. Instead, Elisaveta works as a charlady in some random small village until they have money for train tickets to get to Joey...