Nancy could never have done what she has done without being intelligent and professional, in certain ways and to some degrees. I also think she devoutly believes that she is being a 'good guy' in what she does. I also think she believes most everything she says, but she is clearly perceiving a different reality than do I.

Nancy's bias toward thinking that the "Zetas" are always telling the truth renders her unable to accept anything which would ever prove them wrong. That means she can't be trusted to honestly assess or temper her own views.