The kids keep having to shoulder their parents' immaturity. I can almost see the manga mom logic of her plan, but if she thought Shin was mature enough to be told the truth she could extend the same courtesy to her daughter. Well, I guess she didn't tell him as a courtesy ... still, it's unfair that she's putting this all on him when she and the dad are the ones responsible for this happening in the first place. She's staying true to character, at least. It'll be interesting to see what route the dad goes.