Wait wait wait, you CAN divorce, at least in Warband!! While on the map, type 'ctrl + ~'. Type in 'cheatmenu', then camp. Select 'CHEAT MENU!' and choose 'Divorce Player Spouse.' Boom, she's gone - but she loses around 30 relationship points. My wife had one brother and I lost 10 points after my divorce, so I'm not sure what effects it will have on your family, but I didn't seem to lose any honor or renown.