also I thought about it a little, and went back to re-read chapter 6 where we first see Inoue.. I guess i'm not super worried or mad at her. I mean, it seems like she just wants to be alone with kase-san because they've stayed friends, and wants some competitive spirit between them, that's all fine and dandy.
kind of like how if you want to hang out with your friend and they suddenly decide to bring along a significant other/friend they don't really know when you just wanted to spend time with them.. so I can understand where Inoue is coming from, but she should have been a little less aggressive about it. But because Yamada assumes they dated (which I doubt, like many others here), she's extra tense and probably made Inoue unsettled too.
I just kind of hope this is sort of what's going on, and Inoue is actually a nice person that Yamada might come to like too once things are cleared up or something..