You disagree that a grammar school, which selects based on academic ability, produces an elite cohort?
Depends on how we define elite. I just did a quick google and found this.
[https://www.harrow.gov.uk/www2/Data/Council/19590718/Minutes/009_Education%20Committee_1%20July%201959.pdf]
Ok, these are stats from 1960, but in 1960, the Borough of Harrow had 19 schools, of which 7 were grammar schools. (Assuming each school had the same number of pupils), her school placed her in the top 37% of school pupils in Harrow
I think most people would define the elite as a little more selective than the top 37% or so.
She may hide it well
She doesn't hide the fact she went to Cambridge.
but she's the product of an elite education
Only after Cambridge