RJ did it too; Sanderson was just more obvious about it, I thought. She doesn't have any particular role to play; she's just a shoutout to the fans, especially those who have strangely decided to idolize her.

Also, she's probably as good a symbol as any to the characters' past; a connection to the Emond's Fielders' old life, back in the Two Rivers, before all this. Sturdy as a rock, unchanging, a pillar of strength. Just like what everyone says about Two Rivers folk. Something vague and poetic like that.

RJ probably liked her too, and didn't want to give her an inglorious end, i.e. fading off into the background, forgotten. Killing her would cause unnecessary pages of emotional turmoil for Egwene or Rand or Siuan or someone anyway, and end up a waste of page space. If she's going to die, it'll probably be something at least slightly more heroic, and at a time when no one will dwell on it for long; i.e. at the Last Battle.