jenny didnt stuff up blair and nate's relationship, they stuffed it up themselves. Jenny was just being a friend to nate and trying to be one to blair. and she wasn't mean to elise, she was just being a teenage girl who wanted to be accepted and she finally got her chance. and you can tell she was hesitant at the end, with making elise the new follower. and why does blair get forgiven for all the stuff she pulls, but jenny is hated?
and jenny's not a b!tch, especially not compared to the others on the show. she's just trying to figure out who she is. plus dan would have found out about serena's "pregnancy" eventually and jenny's his sister. she has the most right out of anyone, except serena, to tell him. And jenny didn't kiss nate, nate kissed her and she practically ran away from him. and she was trying to be a friend to blair when she told her the truth.
and it's not the books it's the tv show. of course the characters aren't the same, that would be completely boring if it was.