Finally, I am not a mythical character who has been lurking about Mumsnet for years under different pseudonyms, enquiring about just a single topic.
I never said you were mythical. As for the other stuff, stop gaslighting me. I'm not going to out you on this thread but you and I both know I am not wrong.
Hundreds, I mean literally hundreds and hundreds of posts containing the word 'grammar' have been written by you under 4 different user names going back to 2014 and it's likely there are other other names I haven't spotted. You have a 'style' that is very easy to identify as well as a pretty constant family backstory that you carry with you from user name to user name, changing minor details for anonymity, the sexes and ages of your DC for a start.
Personally I don't believe you have two DDs who are currently studying at roughly the same stage as your GD. That ship sailed a few years ago, didn't it? I think they are being used as a smokescreen here. But it doesn't matter what detail you change, because as always it's the stuff you seem completely incapable of changing that gives you away.
I'm not sure about the granny annexe is real either, but it's too long winded to go into why that doesn't ring true with me. Unless your financial circumstances or living arrangements have changed dramatically in recent years or you've moved in with your parents?
However, your modus operandi and your single agenda obsession (namely state grammar school education compared to non-grammar and private education in terms of attainment and outcomes) comes through like a klaxon every time. Virtually every single thread you've ever started, and there have been many over the years, has been on the topic of education, yet you are not a teacher. Christ, you've even started threads to discuss the results of schools that aren't even in your half of England, let alone your own county. That's just not normal.
I'll lay it on the line here.
My gut feeling is that you no longer have any children of your own who are still in school and you deeply mourn the loss of that. You feel all at sea without it, because it was your comfort blanket. You enjoyed feeling connected to the word of school through your own DC and now they have left that has left a huge void in your life. You no longer have a legitimate reason to over-involve yourself into someone else's educational experience and leech off it for your own kicks.
The fact that this very vulnerable girl finds herself in this predicament and 'needs' you to be her saviour is probably manna from heaven for you. You get to indulge your obsession all over again.
This is about you, not her. And that's wrong.