big mom isn't the main antagonist of the arc that's why oda didn't show her it's also for the same reason that he didn't show her using the adv CoC against law and kidd and also for the same reason that the flashback in pirate rocks was not shown from his point of view:cheers:
Her advanced coc attack is that she use on page one.
‘Luffy and zoro are already stronger than big mom and can win against her just fine.