Interestingly, she seems to stick to the truth in an Aes-Sedai-ish way where possible - the only times she has lied, AFAIK, was when she told Rand that "Moiraine sent me", and when she told Egwene her dress was orange (or whichever colour).

She told Matt that she got the pictures from a Darkfriend, and give that she is BA, this is very likely to be true.

I wouldn't be surprised if she met up with Perrin once more (we'll find out for sure in ToM), and perhaps also with Elayne in Andor to give some guidance in dealing with the BA/Kin.

I think that's what her letters are - she can't betray the BA "until the hour of her death", but she can write letters which are only to be opened after this time.

EDIT:
One thing that really does puzzle me is the scene in KoD where she distracts Rand from talking about Taim. This scene (plus her leaving just before the trolloc strike) convinced me she was BA. If Elza could fight Trollocs, there's no reason Verin couldn't, so maybe she legitimately tried to leave, but the part where she tells Rand that Taim "will have to wait until TG" sounds an awful lot like she is acting under Moridin's or Demandred's orders (whichever is Taim or controls Taim).