Wenduag is really obviously performing a macho, because she grew up in a toxic environment and can't see past the "might makes right" framework
Except there were no such cruelty in the environment where she actually grew up - mongrels are a tight knit community that puts extreme value on the family bonds and and on communal responsibility. Many of them are completely enamored with the stories of crusades and all that duty + honor luggage that comes with it. So the "natural" inclination would be to protect non-combatants of the tribe, not to spit on them.
Still, she is not typical mongrel due to hers chance meeting with Hosilla, who fed Wenduag some demonic rage and made a good little minion out of her. Still, she willingly accepted cultist's philosophy, betrayed her own tribe and was proud to set up similar "accidents" for the promising younglings.
In short, I do not agree that it is environment's fault that Wenduag is dumb, cowardly and selfish bug-girl.