If I was on 90k a year, I wouldn't wear Supermarket clothes and neither would my children. I would pass them on to charity, when I've finished with them, though.
As said, proportionately, she doesn't spend anymore than most of us, do.
We could all be shopping at Primark/Peacocks and using carrier bags to carry everything in, rather than buy separate handbags, but it's nice to own nice stuff.
That dress was beautiful and the silk is ethically sourced, if you couldn't tell the difference between that and the Asda one linked, then you're in denial. It wasn't expensive for a silk Bridesmaid Dress.
I've always apportioned a % of my household budget and disposable income for my children. That added up to shopping at Next etc (good quality when mine were little). I was sneered at, for that, on the Council Estate I lived on. That and me not putting my children in footy kits.
I know other people give their children very little, compared to themselves, but the SIL doesn't feel that way about her DD.
What next, will the family laugh at her behind her back because she wants her DD to have the same quality food as her and takes her to decent restaurants, not just feed her 'childrens type food' in crappy places?
They earn over 3k a week, between them, it's totally their choice how they spend it.