I am surprised that Dior, or any dress design house would want to use the Duchess of Sussex as their 'face' (or more accurately their 'body').
Absolutely, nothing to do with who or what she is, but because she emphatically does not have a model shape and I am always in admiration with the way she dresses to hide a really difficult body inheritance. To put it bluntly she is of a naturally dumpy shape, large waist, short legs and hips too close to the waist. See any photos when the Princess of Wales is in the picture, and thankfully for D of S, these are few and far between, and her figure inheritance is obvious.
None of us can alter the shape we are born with, genes will out. I have the same waist/hip problem that she has, fortunately I have long legs, but, under the circumstances I am surprised Dior are signing her up as their 'face'