RJ never did something like this before in the WoT (e.g. letting Rahvin have a PoV from before his death in LoC, or Sammael having a PoV in PoD). I also didn't find such a plot device in BS's Mistborn series (spontaneously, I don't know any fantasy series, where something like this happens). On the contrary, in his annotations on Mistborn, BS even states that he doesn't like hopping back in a specific timeline, and tries to avoid it (of course, he has to bring Mat, Perrin and some other characters behind Rand's plotline forward). If BS wanted yet another Graendal PoV, it would have appeared in TGS. If we need further informations on Graendal's plot, she will be mentioned by other characters, like Moridin, maybe SH or Aran'gar. This is also supported by BS's statement that only Graendal's name will be mentioned a few times in ToM. Plus, that he wants to make ToM more to work on its own, and not feel like "All of the stuff that didn't go in TGS thrown together" (which a Graendal PoV from before her death would precisely feel like).

All in all, nothing supports the pretty far-fecthed idea that Graendal will have a PoV from before her death in ToM, besides the feeling that it might be "cool".