You assume Graendal divined Rand's intention and prepared for it, but that's counter to what Graendal is said to do. She plans for every possibility. Your idea would have her plan for none except the one that occurred. She's smarter than Rand, she's not omniscient.

The idea that Graendal survived is probably this book's version of "Semirhage planned to get caught all along!" Face it, the Forsaken are ridiculously incompetent and doomed to miserable failure. This theme was made clear through the books, and Verin said it right out in her chapter. Aginor killed himself in a Wilder's mistake of overdrawing on the Source. Balthamel was turned to fertiliser by a walking garden. Be'lal got balefired by someone far inferior to him because he was busy monologuing. Lanfear got tackled to death by a short woman not using the Power, while she herself had an angreal. Rahvin and Sammael were killed due to the intervention of their own allies. Asmodean died so miserably it isn't even felt necessary to tell us who did it, so unimportant it was, he got killed while getting himself a drink. And Semirhage, after getting caught because of an incredibly idiotic plan that was doomed to fail, dies because her priorities were skewed.

Graendal's dead. Her survival would be completely out of character for a Forsaken.

Nor do I believe the Semirhage incident was her idea. Remember that it was Moridin who ordered Graendal to inflict psychological trauma on Rand in the first place. This is quite clearly within the scope of his schemes.