That's Soegi, president of the Calligraphy club, whose design is quite similar to Yamashita's. I hope we get to see more of her (as in, "I hope she appears more frequently", not as in "I hope we get to see her with less clothes" 😫). The band, calligraphy, and art clubs are the only one whose presidents haven't asked anything from the science club as of yet.
Given that this manga has been quite good at foreshadowing stuff, I wouldn't be surprised if we've already been given clues of their future involvements before they were actually introduced.