Ok a fashion pedant post 😂 re: posters citing “couture”.
Designer clothing and Haute Couture are very, very different.
You can buy designer clothing from brands like Armani/Dior/Channel but these are simply from their ready to wear collections - you can walk into any of their shops (or websites) and buy off the rack.
In the case of Armani ready to wear it’s labeled “Giorgio Armani” (which is the label M displays in the picture). Retail price will be circa £3.5K.
Haute Couture is a very different beast. Any clothing produced as HC has to meet very specific requirements, from the construction methods (seam treatments, stitching etc), number of staff in the atelier and every garment has to be custom made for the client , requiring multiple fittings.
Armani HC is labelled “Armani Privé”. A couture AP jacket will cost between £10-20k (even up to £50k if it’s sufficiently embellished with bespoke embroidery/beading etc).
So, yes her jacket is designer and expensive, but it’s not couture and anyone (willing to part with £3.5k) could buy one.
The fit is exactly (unless she had it altered - but it looks as if she has not) what it was when she acquired it - same as any of us buying a jacket from M&S.
Buying a designer jacket doesn’t mean it will look great if the fit is poor. As a pp noted a person would be far better off spending half the amount (or less) on a higher end high street/lower end designer item and having it tailored to fit in terms of how “expensive” it looks when worn (again as a pp
noted why you see other royals rocking “high street” items and looking fabulous I’d bet in a lot of cases they’ve been altered to fit perfectly).
That said there are a cohort of people who covert the label above all else, even when the item is not especially flattering.
Either way the main point 😃 is that the jacket is not couture. It’s just an expensive ready to wear piece of clothing.