I'm guess kaguya had some tragedy during the war... She probably lost a baby or two. Because of the trauma of miscarriage or the like, she decided to eat the forbidden fruit in hopes of ending the war that took what's most precious from her (why else would she go eat a forbidden fruit if not because she was traumatized by the war...?). All that power she got from the fruit, ontop of her PTSD, made her go mad. Now she's treating the entire world like her playground with white zetsu's as her children. The chick's just insane.