'Girl' -- You mean a full grown adult, that is married and has a full-time job. As in not some teen kid that is changing schools, jobs every few months, a person that is in a steady relationship, having steady employment and doesn't move around a lot. She is pretty much settled.
Both of them take advantage of Sophie for different reasons, but I wouldn't necessarily call them inherently bad people.
Just because Zack sleeps around while not in a relationship as a young adult, doesn't make him a bad person, yes he makes some choices that could be perceived as dick moves, but does that make him 'evil'? Personally I don't think so.
It is Sophie, the full grown adult, that made vows with her husband, that is sleeping behind his back and made the choice herself to continue doing so because she enjoys doing it. She even goes out of her way to mess with his head while doing so, by making phone calls while moaning and shit.
Yet you call her 'just a victim'? Lol, she is more evil than Zack and the principal combined. The only way she's a victim is because of circumstances at the start, but afterwards it's her own choice to continue without coming clean to her husband.
If she truly was a good and honest person, she would come clean and divorce her husband....