Well this article touches a bit on her "visions," but doesn't exactly come out and say she had plotted this as the aag from Texas stated.
http://www.courttv.com/trials/yates/background.html
But it does mention the fact that she had these visions for quite some time and how she worried about how her kids would turn out...which goes to prove this was not a spur of the moment episode.
This was an illness that went untreated for many years and in my opinion she should be sharing a cell with her husband and any and all doctors and psychiatrists she shared her "visions" with.
http://www.courttv.com/trials/yates/background.html