Oh, derp, you already sort of answered my Sybelle Spicer question. But how would she secretly communicate with Tywin? Surely Robb’s men took control of the ravens? And given the flying time, and so on… I just don’t see her getting assurances from Tywin prior to the wedding. But maybe I’m wrong.

If the maester in the castle is more loyal to Sybell than Robb, it’s kind of hard to prevent her from secretly communicating, because a maester with decent sleight-of-hand (and most maesters, from Luwin to Cressen, seem to have some) can easily swap out messages and fool any surveillance. 

As for assurances, we know she got them:

“I made certain of that, as your lord father bid me.”

“Your lord father promised me worthy marriages for Jeyne and her younger sister. Lords or heirs, he swore to me, not younger sons nor household knights.”