I can believe her measurements because with the structure of her legs/hips, her hips only really jut out at the bottom and are angular as opposed to curvy. So, when she's standing straight--or at least somewhat straight because Holly does not post a single photo where she isn't posing her legs in some way
--her hips are not too pronounced (photo on the left).
Even in the second photo where she's arching a bit (hence the thigh gap) to make her hips more pronounced, you can see that when you cover the very bottom of her hips that they aren't that noticeable. Kim Kardashian has similar measurements to Holly's but Kim's hips are well-founded and flare out, so it's a very different look:
Holly is therefore doing some serious contortion in the photos where her hips are very rounded and popping (if not outright editing in some). Regardless of whether or not she's had work done to her body--which I wouldn't doubt--her photos are still deceitful because her hips would look nothing like they do if she stood upright casually like a normal human being. I'm pretty sure of this because I have a similarly shaped lower body, except my waist is almost 4" smaller than hers and I have a greater difference between my waist and hips, and it still takes a highly unnatural pose to round my hips and make them look much greater than my waist like in a handful of Holly's photos. I tried in front of the mirror just now for five seconds and it gave me a leg cramp. I can't imagine how ridiculous she must feel doing this for every photo
There's also no way in hell that she fits sz 0 in Abercrombie jeans unless they are a pair that runs large or stretched. When I was 124-126 pounds (which I think she said was her weight) my waist and hips were 2" smaller than hers and I couldn't even pull a sz 0 from Hollister (whose parent company is Abercrombie) past my upper thighs LOL. Also I highly doubt she's wearing XS bottoms without half her butt hanging out, but that's Holly's style so