Technically speaking, 100k yen a day falls under US federal minimum wage if the day in question lasts longer than 12 hours, and since I assume she's going to be there every day off from office work and post-office work hours, she'd better make sure she keeps that office job if she wants to be able to maintain the spoiling of her newly acquired "little sister."
I feel like there's a chance for drama here. Meguru's clearly projecting someone onto Kasane, so I'm sure it'll cause some drama in the future. Maybe if that someone comes back?
Lemme get my prediction in now. Meguru had a crush on her actual older sister, but since her family is currently out of the picture (for reasons that may have caused the sitting out in the rain scene) she's lonely and wants to replace said sister. Who I'm sure will come back and be the primary cause of drama.