Unless they could cure her hunger rampages, I believe that would have prevented her from becoming an Admiral.
Imagine Big Mom as an Admiral and then she randomly gets her hunger rampage because she is craving for some food, and then she starts attacking and killing everyone including the Marines soldiers.
Imagine Big Mom as an Admiral and then she randomly gets her hunger rampage because she is craving for some food, and then she starts attacking and killing everyone including the Marines soldiers.
Alternatively go the Garp/Sengoku route and have a lifetime supply of crackers stowed on the ship.