Just finished reading the book and I'm going to come out and say it - in the show Catelyn Stark comes off as a heroic figure, but in the book she's just a stupid, stupid evil bitch.
The way she treats Jon Snow and sends him off into celibate exile is just plain spite - at her husband. Jon shouldn't have had to pay for his dad's fuck up.
Then, going ahead to Kings Landing the way she did put pretty much all of Winterfell at risk - when she could have easily sent anyone out there with the fucking knife.
But, once she did go out there with the knife kidnapping Dwarf Lannister is a completely and totally stupid and vengeful move. The Dwarf was fucking heading to King's Landing - where her husband would have been able to deal with him legally.
Instead she grabs him - which is guaranteed to start a war in which many of her people will die and her children will be at risk. Even if she had brought him back to Winterfell instead of bringing him to her insane sister it still would have sucked. Because if she tried and convicted him at Winterfell there still would have been a war.
The only way to deal with things and not have had a war was to let him be arrested and questioned by her husband in King's Landing. But, instead she splits the entire seven kingdoms into three separate warring kingdoms.
Everything she does is selfish, misguided and dumb.