I would only go the Skymaster route if it were the only way forward. I have nothing against the Skymaster - but she can already fly the DA42 competently, and I think it preferable that she continues with a conventional retractable twin with glass cockpit, FADEC etc as that is what she is used to on the Citation. Moreover, we have access to a DA42, and there is an FTO nearby that operates them.
Is the "UK only" a JAR requirement? Or is it a CAA requirement? I haven't heard of that limitation before - how do really small JAR countries (eg Luxembourg) issue PPLs if all the training has to be in their airspace?