I think it's important not to let the very last line distract you from everything else she said in that page.
I'm thinking that Inoue came back for the school festival ONLY to race Kase one last time.
She says that she doesn't know what Yamada is thinking, due to her never having joined a club, I see it as a "you never had the chance to have a real rivalry" kind of statement.
I believe the request for Yamada to stay out of their way is her saying that her rivalry with Kase is a very personal matter to her. She wants it to stay something exclusively between Kase and herself, and not have anyone else involved.
I think Inoue is very passionate about her perceived rivalry with Kase. I wouldn't be surprised if she demands Yamada leaves during the race and Kase goes along with it (we all know how clueless and tone-deaf Kase can be ;p)
I see this lasting another 2 chapters, with it being resolved at the end of chapter 21.
edit: looking back at page 16, the fact that she starts saying "I.." and then switches to "Kase-san always saw that on the way home from school." actually makes me think that Inoue pointed Yamada out to Kase on their walks home, and then that's when Kase actually started crushing on Yamada. I'm starting to think Inoue actually knows Yamada is Kase's girlfriend, or at least suspects it.
What this means for Inoue's feelings towards Kase I have no idea, but it does make me think that she knows Kase could be distracted by Yamada while they run.
last edited at Aug 24, 2016 3:08AM