Sara, girl, what the heck. Also I was surprised she asked it so quickly, I know what I said last chapter but I was expecting it to actually come to surface after some 4 chapters of weird tsundere shenanigans.
I really want Sara's reaction to not mean she liked Mimi but there is no other way to read it. It would be fun to see her as a chaotic wingwoman, opposing to Iwao's yuridanshi fading in the background role.
P.S: Little bro is right to bring that up, she should be conscious of that and know that those boundaries need to be established. However, from the reader's perspective I truly think Sensei already sees them as two different people. It's "my oshi who I stan so hard" and "the girl behind my oshi with quite a different personality". Might not be so clear right now, but at least subconsciously this dictomy. already exists.