When do you imagine Sybelle Spicer negotiated her deal with Tywin? I always assumed it was after Robb amd Jeyne slept together/wed, to try save the situation

I think she opened negotiations the same day Robb was wounded taking the Crag, if not the same hour, and I’m pretty sure it was only the fear of reprisals that kept her from offering to assassinate Robb in his bed. 

In other words, definitely before.