That Jenny's character did not change just because she has sex with the MC, I like most. She do not like him much and especially uses him that makes the relationship special in the game, changing her character overtime, would make their relationship boring. She would be only a Roxxy variant.
For the same reason I do not need Annie likeable. If she has ever sex with the MC, it should be, because she thinks she protects the pinciple. And like the sex in the aftermath the sex with the MC. It just should not be blackmail. Maybe she tell him later why she had sex with him and he said he wanted to harm the principal, even if she sucks.
I see no reason why Mrs. Smith is 'not DC's best work'.