User blog comment:Kaido King of the Beasts/Chapter 857: The Art of the Deal/@comment-24850639-20170302134046/@comment-5398287-20170303001319

I don't know that Big Mom is necessarily as cautious and wary of others as certain other pirates (Crocodile, for example). Yes, she can predict things like Sanji's crew coming after him and plan accordingly, as well as set up a fairly thorough plan to kill a notorious family of killers leading the world's preeminent Terminator army, but she's demonstrated considerable underestimation of people not "at her level" or whom she believes are on her side a few times. For example, she apparently didn't even try to keep tabs on Jinbe after he refused to spin her roulette wheel of death, she didn't keep a larger and/or more powerful guard to oversee Luffy and Nami's imprisonment, and there's nothing to suggest she or her children think the Vinsmokes, especially Sanji, have any plans of their own to turn tomorrow's events in their favor. That doesn't necessarily make her dumb, but she's got a history of not considering all the options that makes her choice of Bege, a fairly smart upstart pirate whose style and tactics fall right at home with hers, to guard the wedding a logical one.