From a literal standpoint it only makes sense that Graendal was killed by Rand. The "Graendal somehow survived"-theories (which remind of the ideas that Sammael or Osan'gar survived somehow) would be an unnecessary twist such late in the story. Considering that RJ wanted to wrap up things, it's clear that Graendal was balefired in a powerful scene, because she wasn't needed anymore and to emphasise Rand's hardness. As it is made clear in the book, Graendal simply couldn't predict that Rand would "punch her in the face" in such a way.

Besides that, Graendal tells in TGS, prologue, that Aran'gar doesn't know where her lair is. Thus nothing suggests that Aran'gar would go to Graendal (Aran'gar can certainly find other, more neutral refugees).