Chuckle to your heart's content, your ignorance and lack of perception is no fault of mine. How people arrived is very much to the point. Members of Commonwealth nations are free to move from one Commonwealth nation to another with an ease which would-be immigrants from non-Commonwealth nations do not enjoy. How her parents arrived in England is very much to the point. Had her parents attempted to enter the United States, for example, it would have been very much less likely that they would have been admitted. Within the confines of the Commonwealth, they just needed to get on a plane--all they needed was that price of admission.
Immigration, despite your simple-minded expositions, is neither simple, nor subject to universal descriptions. In Germany, for example, the Turks who came to get what were, relative to the economy of Turkey at the time, good paying jobs are not German citizens, nor are their children German citizens even though they were born there. However, someone of German ancestry from any country in the world could arrive in the FRG (i.e., "West Germany") and immediately claim German citizenship, and would be granted that citizenship upon proof of their ancestry. This case is extraordinary in the industrialized nations. France faces a situation similar to, but not identical to, the British Commonwealth. Citizens of nations which were formerly French colonies cannot automatically get French citizenship, but the hurdles for them are much lower than people from other nations who might wish to become French citizens--usually it is just a formality. There is, of course, no French equivalent to the Commonwealth, so they can't just get on a plane, fly into Paris and settle down.
That is, however, a pretty good description of how it works for people migrating within the Commonwealth. So how her parents got there is very much to the point, whether or not you know it.