Okay I'm not able to piece it all together but here's what I was able to find:
The management dude above them gave them something important to work on that was above what they were capable of. It seems like Kuroda is calling in favors and is snooping into what's going on politically behind that decision, or something like that--at this stage, maybe it's blackmail? I don't know enough about Japanese officeworker culture to figure it out exactly. But I'm confident he intended for them to fail for some reason that I'm sure we'll find out more about.
Anyway, Shirakawa notices that Kuroda is doing things on the sly and gets suspicious about her. I think she's also feeling slighted because, though they have the same amount of time in the company and are being compared/implicitly put against one another, Shirakawa is supposed to be the senpai--and yet that position isn't being respected, both by the immediate assignment of difficult work and Kuroda doing things she hasn't been taught. It seems like she thinks Kuroda is doing sketchy/suspicious stuff and maybe trying to get others to do the work for her, or secure her position through office politics so everyone else will take the fall instead of her.
I don't know what feelings are going on with them, but I know internalized misogyny and repressed lesbianism mixing within high-strung, high-achieving prideful women is a really common driving factor in Sal Jiang's work, so there's a number of directions this could be going. I feel like the snipes back and forth they make after getting told off are important, but I can't figure out all the emotional context.
I can't tell if Sal Jiang was just focusing on the twisted feelings here and didn't intend for us to understand the politics at all, if they're mishandled, or if we'll find out more later, but I look forward to finding out!