While eavesdropping, Aya discovers that a story she was pursuing turned out to be a petty scheme by Megumu. (Lotus Eaters #38)

That said, Aya being sad about it is mostly the artist's own interpretation on the scene; Aya already believed the tengu were behind it and intended to do a little whistleblowing, and so in my opinion, her reaction is the manga is more one of fear/shock because Megumu's literally going "I know none of MY subordinates would be STUPID enough to WRITE ABOUT THIS". Aya's exact thoughts aren't really spelled out, though.