I would argue that the rare moments we see behind her mask are the moments that humanize her. Jasnah presents herself as eminently composed, knowledgeable, and rational. But as readers, we know she doesn't really feel that way all the time. We get to see her insecurities about her research of Urithiru and the Voidbringers not being meaningful despite her best efforts. We see how exhausted she is at the beginning of WoR, and how behind the 8-ball she feels when she shows up in OB. We see her struggle between her rational mind recognizing Renarin as a threat, and her heart recognizing him in love. Yes, Jasnah often appears perfect, both to the reader and the other characters. But what humanizes her is that we readers are shown that she really isn't perfect. She's trying just as hard as everyone else.