Just something interesting about choristers that would seem to give some insight into Grace's character:
https://www.schoolhousemagazine.co.uk/education/music-to-my-ears/
" ‘It’s a very normal way of behaving here,’ says Murray. Choristers, he says, are one-of-a-kind. ‘They’re eloquent and they tend to use time efficiently. There is a civilised thoughtfulness about them.’ Being a chorister has a ‘growing up’ effect on a child. ‘They are pocket adults, more confident than their peers, and socially sophisticated.’ "
" ‘You are able to present yourself with a bit of confidence. Musicians tend to be bright people, but it gives them an edge if they are able to demonstrate that they can keep a few plates spinning.’ "
If this is the "you're so great!" narrative kids like Grace are fed, there's no surprise in her being such an egotistical, "what-I-say-is-fact" type.