I like your theory. I'm going to have to go back and re-read the scenes with Tsutama, but, to be honest, she sounds like she fits the bill perfectly. One big thing that I'm curious about: was she mentioned during Egwene's Oath Rod scene in the White Tower? If she's explicitly listed as declaring an oath that can be easily misinterpreted (i.e. "I am not of the Black Ajah"--technically true of a Forsaken)--then I'd say we have a winner, unless someone can offer some alternative evidence. In retrospect, Tsutama indulges herself in rare and expensive items (AoL items?), returned more ruthless and her personality is a little off.

It will be interesting to analyze the sisters she sent to the Black Tower. It's obvious that they were almost all selected for their like for men(Jezrail: almost married a man; Melare: supports her grandnephew's education) but there's a few oddballs in there ( Pevara: heading the BA hunt; Desala: hates Darkfriends with a passion--sounds like someone with easily manipulated psychological problems; Tarna: pillow friend of a known BA, Galina).