I guess it doesn't, but there is the same evidence against Slayer as there was before. Basically that we knew very little about what he could do before book 10, and it was supposted to be obvious in book 5 who did it. As far as we knew at that point, slayer had no way of getting rid of the body or any of several other problems. Also, in book 10, when we get Slayer's POV, he thinks with pride about killing the two BA in tear back in book 4. But doesn't think about the Forsaken he killed?(under this theory). Really, there is no reason to go there. Just accept that Graendal did it personally. It makes sense that she was there. She had means, motive, and opportunity.

Also, from ToM, Graendal doesn't seem to have worked with Slayer much in the past, but i don't think that is explicitly stated.