Yea I was thinking that it most likely is the grandma (that broad knows how to play all sides) but it got me thinking a few weeks ago. If Joffrey dies, who then becomes the new king. Is the new wife in charge of all the lands now or does it go to the next man in charge which would be the brother of Joffrey's dad who technically is the rightfull king anyway? Or wait, if it goes brothers then does that mean Jamie is the new king?
Those that want to answer, make sure you don't give anything away from the books.