Oooh that's interesting Dave. Then as a non-royal she'd definitely need a Visa to enter UK, with a time-limit on it.
My only concern now for the pair is the question of security, and who pays for it. They'd need a large team of trained protection officers, as kidnapping (particularly of the child) and robbery etc are distinct possibilities, sadly.
I thought the Queen's statement (publicised on the TV News) was very charitable and understanding. It's obvious she wants to avoid a huge rift, and to reassure them both she understands their wants and needs.
Of course, this would have been composed by her team of advisors/speech writers, but it sounds sincere to me.
Ah well, onward and upward!