BS even said that he doesn't want to give a "Graendal is toast"- confirmation "yet" (but after ToM, he will), that only Graendal's name will be mentioned a few times in ToM , and that after the book, we will know her fate.

This strongly indicates that other Forsaken will muse on Graendal's death, like e.g. other Forsaken mused about Sammael's death after ACoS. Nothing suggests a Graendal PoV in a flashback; it's most unlikely.