It's her hunger. Ciphrang are defined as Hunger. Her desires, the fulcrum of her soul (that which drives the very core of what is Serwa) is centered on using/devouring other souls. That she has not been doing this long is irrelevant; she is the type of soul that Hungers enough to feed on other souls in the Ciphrang way in the Outside.
EDIT: To elaborate, while I still hold on to this drunken thought, I was disappointed we never do get to see Kellhus under the Judging Eye. I suspect he would not be damned in the way other Dunyain are (though probably for other reasons, i.e. the Hundred's despisal?). It's a supreme self-centered nature that drives the Ciphrang. Whether his subjects are treated poorly or not doesn't matter to him, to be fair. "Good" and "evil" are irrelevant to his objectives, at least regarding the means he uses to achieve them. In the end, Kellhus can loosely be described as altruistic. His base motivations, why he went through all he did, really was to "save the world." Not because he is soft-hearted about them, but rather because he truly believes the world being Shut is a bad thing for the Dunyain mission (read: a bad thing for people not-Kellhus). He uses other people to accomplish this, but it's a meta-self interest, rather than self, that drives him.
Even his willing exile from Ishual wasn't for his own interest; it was deemed necessary for the Dunyain as a whole.
Serwa is entirely interested in Serwa, and what she can glean out of her circumstances.
Re-EDIT: Kellhus describing himself as "descending as hunger" in the Inverse Fire is an extremely blurred line between Ajokli and Kellhus. Maybe that is his damnation, if the Kellhus personality is damned?