Charlotte Linlin, more widely known as Big Mom, is a very powerful entity and has proven that she deserves to be called a Yonko. Her physical prowess and Devil Fruit mastery is almost unrivaled and very few can stand against her.
She was able to knock back a Kong Gun with very little effort showing a supreme mastery of Armament Haki.
She also possesses Conqueror’s Haki.
However, everything I just said goes out the window because of her mental state. Her mind is very fragile and at the slightest disturbance of hunger or sadness, she goes flying off the handle and destroys anything in her sight. This along with numerous other factors have caused nothing but embarrassment to the Big Mom Pirates and she only has herself to blame.
Her willingness to murder her children for the slightest mistakes is another fatal flaw. She killed one of her sons for simply being in the way of one of her rampages and it cost him his life and for this reason Opera didn’t inform the others about Luffy and Nami’s escape, he kept his mouth shut because he knew that if he told the truth, Big Mom would kill him on the spot.
This set a chain of events in motion that allowed the StrawHats/Bege Alliance to cause so much damage in the first place.
Had Opera not feared her like he did, he could have informed the others and the threat could have been neutralized in no time. Big Mom bullying Pudding caused her to switch sides last minute and join up with Sanji, causing even more problems.
Her state of mind is quite possibly one of the worse flaws to her character seeing as depending on what state she’s in, she can be a criminal mastermind or an incompetent toddler. She was able to put a beautiful plan together that would have allowed her to not only get rid of Germa, but also acquire all of their technology.
Once Mother Carmel’s photo was broken by Brook, all of her ambitions went out the window and she had lost her grip of the little sanity she had left.