Nothing like an existential external threat to kick up some infighting! But, this has allowed us to learn more about Himari's true ability. I was as surprised as Yuuki when she said her real ability was to copy others'. I wonder what makes some abilities compatible vs. others that aren't. Also, I wonder whose ability it is to create all those weapons that she typically uses. I bet it must be a whole ordeal if she were to break her phone, can you just swap out sim cards to a new phone and use that?
In any case, Yachiho is a very easily hated character, so, if that is what the author was going for, then great job. I was trying to think of some way in which you could frame the way she treats Himari to be well intentioned, but I am struggling. So, until proven otherwise, I am going to view her as essentially a heel meant to help Himari grow and mature at the moment.
I loved how the Anti-Demon Force otaku that creates the force field was gushing over the magical girls around her...wait...wrong show. Her ability seems mighty convenient for these types of events. I am guessing she might not be an important recurring character, but instead a bit of a walking plot device to enable this tournament(?) to happen.