I've always assumed it would be Alivia, who I think people have forgotten about since she hasn't been seen since Winter's Heart even though she's been traveling with Cadsuane and Rand the whole time since. Min's Viewing said that Alivia would be important for the "help him die" prophecy/Finn question. Elayne is obviously out because of the pregnancy (and I'm still disgruntled that Rand doesn't even seem to be aware of that), and Aviendha probably will be as well with her Rand-reunion in AMoL ( ) even if she's not too busy being a Wise One trying to help "save a remnant of a remnant".