Milton is not human nor distortion and was actually created through a test tube by a man named Dr. Schrodinger. Infact she is not the only one as there are other human animals hybrids in the labatory. The lab is found hidden deep underground in district 11. Milton wasn't really mistreated but had to go through slot of trials and test to become the perfect creation. Milton usually was in a very cramped containment with not much room to move around. Despite her brash and vulgar personality, she's in denial of her existence and constantly questions her identity whether if she's here or not. (This hints of the Schrodinger's Cat ideology, whether it is dead or alive). It is unclear how Milton left the facility but is a very fast learner and adapted to environments, learning behavior from anybody close to her.