I was thinking that this isn't a pose that makes her look smaller, yep.
On the one hand, it makes her look "large and in charge" and maybe that's a vibe she's cool with.
It's not so much "this pose makes you look fat" in the way that standing with hips square to the camera, say, does. As a previous commenter pointed out this is a "power pose" (love that phrase, never seen it before) which plays into her physical size, and emphasizes it. Hence, it's more about the vibe than the actual composition. The actual composition actually de-emphasizes her hips quite a bit.