That might work, although I doubt it's the case. And she rarely acted out of character, except on one or two occasions. And if Odium did send an Unmade to pose as Dalinar's wife, he most likely would have sent one more likely to obey, even if less intelligent. Except Odium thought Sja-anat was completely under his control, well, pretty much, until she transported Kaladin, Shall an and Adolin to the Cognitive realm, instead of killing them.