With the MC mentioning her older sister, I predict she'll show up in the story and be a "classic" siscon. Not the gross type, but the way too doting and protective of her younger sister type. She'll exhaust herself trying to run interference between MC and her love interests.
It's going to be super fun to see all these different heroines trying to sweep the MC off her feet. I'm surprised there aren't more comments discussing this since it's off to such a promising start.