- She ruled for 30% of the time since the American Revolution
- She oversaw the largest reduction of landholdings of any empire in the history of the world. Notable because it was also one of the most peaceful transitions in history -- Australia, Canada, South Africa, Israel, Egypt, etc.
- She oversaw the loss of Sterling the world reserve currency and the rise of another (the USD, EU).
Technically there is no one who could authorize that split except the current monarch. I'd imagine things will continue just as they were
That said, there is precedent. Victoria didn't inherit Hanover, which had been in personal union with the UK, because it had different succession laws (which excluded women). So it's just a matter of political will really.