I might be wrong about this, but my impression was that Asha is very dependent on Kyra for her status. Other raiders don't touch her because Kyra is their leader, and she's her sister; they don't necessarily respect her on her own merits. Moreover, judging from the fact that raiders typically go for easy targets, it's possible that her encounter with Zaton was the first time Asha experienced real resistance. The raider trio even seem to acknowledge that they've never faced a stalker and don't know what he's capable of, and it's only after Hazim eggs them on that they actually decide to risk it and fight.
Also, again, biting Zaton's dick off would be guaranteed death. It's not because someone is used to killing and seeing people die around them that they value their own lives any less.
My point is that even if it's convenient for Asha to turn fully submissive the moment she encounters unforeseen adversity, it's not less realistic. People can have different reactions to the same situation—another person in Asha's situation might have fought to the bitter end, and yet another person might have tried to bargain another way (kind of like Asani does); all these reactions are normal, equally “valid” human reactions. Therefore, it's not a problem if the storyteller chooses to use the one most conducive to the story they want to tell.
As an example, the story of Othello only works because Othello is distrustful and prone to anger. Hamlet only works because Hamlet himself is an indecisive nervous wreck. Indeed, if you switched the two characters, basically every problem in each story would resolve itself instantly. Yet, because both these characters are believable people, and Shakespeare was looking to write tragedies, it's perfectly acceptable for the angry one to end up in the narrative where anger causes the tragedy, and the nervous one to end up in the narrative where indecision causes the tragedy: it's simply Shakespeare utilizing different real human personas in order to tell the stories he wants to tell.
IDK if I worded that clearly enough. If not, sorry.
Either way I consider it, it's just a bad idea to stick it in crazy's mouth. 
