I believe this is how Saki will resolve:
"But you DO have a sister, Teru!" Teru was pretty sure she didn't, and she wanted to read her Kouko Sukoya Super Love Edition manga. But this was the fourth or fifth time someone had bothered her about it. With a sigh, she put down the doujin and looked up at Awai. "Okay, who is this sister?" Awai was shocked but said "Saki." Teru held her cup out and said "but who is she?" Finally after 15 minutes Teru slapped her forehead. "I did have a .. cousin named Umeshu .. or maybe a mother?" Awai helped her out by also slapping her forehead hard with her fist. Hisa brought in Saki, and the two scatterbrained sisters had a good laugh and a hug. After a few minutes, Teru said "Wait, why are we hugging, am I your girlfriend?" "Saki looked down at Teru's chest and said, "I don't think so" Saki was right, the whole thing was a misunderstanding after all! And Kiyosumi won the nationals!