In my opinion, it's the perfect thread to leave unresolved. It doesn't carry much relevance for the greater plot, it doesn't include any major characters and it's something that'll keep some fans guessing forever.
I can't find the source where RJ or BS said we aren't going to find out, but it's discussed here: http://www.tarvalon.net/phpbbforum/view ... =36&t=3219
Ah. I think RJ mentioned somewhere that her disappearance with Merilille is a question we're not gonna got an answer to, so I don't think that has anything to do with the 13x13 turning.
In my opinion, Mierin is the least likely candidate. I think people are being forced to turn at the Black Tower, though, and that's plenty enough.
I don't think any really important characters are going to be, or have been. Unless you count Tarna as an important character, for instance.
I think she's just an extremely selfish person who doesn't really care about anyone but herself. I don't think she loves Lews Therin or ever did; I think it's precisely what LTT himself said: she only loved him for his power.
The difference with her and Elaida is, in my opinion, that Elaida...
His last sentence seems to indicate that she went over the Shadow willingly. If she was "ripe for the Shadow's plucking", I don't see why the Shadow would go through the trouble of forcibly converting her. Much easier to just recruit her, isn't it?