I got this theory after reading [link=(Leigh Butler's)]http://www.tor.com/blogs/2012/12/a-read-of-ice-and-fire-a-storm-of-swords-part-11[/link] first read of Storm of Swords yesterday. Jeyne Westerling's grandmother was a maegi. What if she passed her knowledge down to her daughter, Sybell Jeyne's mother.Sybell seeing the Robb was wounded taking the castle slips in a potion into a drink for Robb and has her daughter take care of him.
I always thought it a little odd that the daughter of the castle he just conquered was taking care of the King of the North. I think Sybell made sure her daughter was around Robb a lot, so that when the potion would make him act rashly around her and ruin everything.