I am not sure if Nien Cheng would act like the Guards because it would depend on her class status. If she had a black class status, she probably wouldn’t act like the guards because she herself would get a taste of what the guards do and lose her wish to become one. Also, if she had seen them raid a house and kill someone, she would probably not join. But if she had a good status, she might join them and act like them if she didn’t know what they really did.