As she isn't a POV character at any point thus far, we don't get into her mind at any point, but ultimately all of our impressions of her come from either Catelyn (Pretty but disinterested in the happenings of Renly's court) and Cersei (who sees her as a beauty who is angling to usurp her role in Joffrey's life, then…

(somewhat spoilery for Storm of Swords/Feast for Crows) Kind of disappointed with the narrative decision to make Margaery Cersei V2.0… My impression in the books was that all the scheming attributed to her was either in Cersei's mind since she was a threat to her or trumped up in order to replace her as Tommen's…