Niffty's twisted mind is caused by the internment of Japanese Americans during WWII. Niffty is confirmed as an American and it's not far fetched to assume that she's of Japanese heritage (with 'Clean it up' song)
She died in the 1950s, presumably in young adulthood. It means that her formative years were spent in a concentration camp.
During the second world war Americans of Japanese heritage were forcedly removed from their homes to the concentration camps (located mostly in deserts) due to an executive order 9066 signed by Franklin D. Roosevelt. These people were classified as a threat to the United States because of their heritage.
Internees were prohibited from taking more than they could carry into the camps, and many were forced to sell some or all of their property, including their homes and businesses. At the camps, which were surrounded by barbed wired fences and patrolled by armed guards, internees often lived in overcrowded barracks with minimal furnishing.
For four years Niffty would live in an overcrowded barracks infested with bugs and rats. People around her, perhaps her own family, were suffering from typhoid, dysentery and food poisoning. Food was scarce as well. All this, while being constantly questioned on their loyalty to the USA.
No surprise Niffty has one screw loose on her.
It also explains how she, on the one hand, can endure grossness as champ, and wants to annihilate any pest she can see. Perhaps it was her only way to control her environment during those 4 years?
