I think you're giving much more credit to that poster than she's due. She didn't point out any hyperbole (her post wasn't as measured or thoughtful as that. She was simply rude - & quite aggressively so?
Her post was deleted by MNHQ as, I assume, they considered it as unpleasant as I & several others did. Enough to have broken their guidelines. I think the hyperbole was all hers, in accusing @SkippitySkoppity of lying (???), trying to make a joke for the benefit of other Mumsnetters, & being "sad". I can't quite remember the wording, but I've paraphrased it much more politely than her actual post.
As for the post that she attacked, I don't think @SkippitySkoppity saying that the sandals "give hints of poor Victorian invalids wearing callipers to correct their rickety legs" is meant to insult people with disabilities. It was a reference to the stereotype of the sickly invalid or pauper in Victorian literature. They're portrayed as wearing too-short dirty trousers with raggedy hems, pale & malnourished, with a severe illness &/or disability (coughing blood into a hanky, on crutches or in callipers).
To me, I read it as an instantly recognisable visual comparison to an outdated medical device - one that is, thankfully, now mostly superseded by much more effective ways of addressing bone malformations. Rickets are thankfully rare now too!
So that visual comparison did amuse me - not the thought of children having to wear callipers. However, @Slothlydoesit , I'm sorry if you were offended not just by that post, but by my being amused by it.
I am genuinely interested in why you find it offensive, though? As you obviously read it entirely differently to me!