Aran'gar seems implausible given the presence of a number of male channelers in Perrin's vacinity, unless she manages to take them all out in one fell swoop. A female Forsaken strikes me as unlikely too, as the Wise Ones would presumably be onto them fairly quickly.

Could it be Fain? If so, I do hope he doesn't end up dying a senseless death for the sake of building up Slayer's villainous creds, Mordred Deschain style.