In fact her entry into the series was completely centered around the events that eventually lead to Asmodean's death ... IMO Sammael was a red herring for Asmo's death which is why RJ kept saying "all the clues are in TFoH" and "Intuitively obvious" etc...

If she is dead it would explain why RJ struggled with figuring out a good way to blatantly insert the information into the story line. But IIRC BS has also stated the Graendal will still be in the storyline for ToM, maybe not as a POV Character, but she could still be in a scene with Moridin or Demandred and admit to killing Asmodean. Perhaps when the FS learn of Semrihage's balefiring she'll bust out with "well that makes 4 of us BFed ... did I mention I zapped Asmo in Caemlyn??"

More likely for something like this to happen than to have Slayer suddenly say "Oh yeah, and I killed Asmo" when that opportunity has already been there and passed up!

She had plenty of reason to kill him off since we also discover in TFoH that Asmo knew her location and had clearly met with her prior to the events of TSR. She was involved in the Caemlyn plot, coupled with her knowledge of events so quickly after they happened it seems like she was nearby.