The relationship between Hester and Jesse was strained from the beginning... even before they knew it was Jacks baby her mother hated her. Because Jesse loved her father more, and had been treated so poorly by her mother, there was a very slim chance Jesse would want her mother included in her life.
Because Meg was so easily manipulated by Hester, and relied on her guidance so heavily, she was the perfect sister to save the her from poverty.
I think people would start asking questions if both parents had dark hair yet the child had fair hair... genetics people