Margie was the principal of St. Rita's Preparatory School, who attempts to turn all the boys on the planet into girls do to the fact being teased by her brothers. The young Margie of present day was given the technology and instructions to do this by her future self, Madam Margaret.
In Operation: F.U.T.U.R.E., when Numbuh 4 was sent to her school, he was surprised to learn that it was an all-girls school before she and her minions, the Girl Squad, revealed their intentions. Wally narrowly escaped with his gender intact, but with his hand turning into a female's.
As a result of him losing this fight, Madam Margaret was able to successfully take over the world and turn almost all the boys into girls. In the distant future, Numbuh 4, now an old man, had formed a rebellion of boys known as The Boys Next Door, who fought against Margaret's forces. When they went to have their final battle with the girls, along with a defector from the Girl Squad, Sally Sanban, the Boys Next Door were overpowered and all turned into girls, except for Numbuh 4, who was confronting Madam Margaret in her lair. Now the last boy on the planet, Wally used the same time machine the villain had used to contact her past self and went back in time to warn the KND about his future. Madam Margaret tried to follow him into the past, but Sally destroyed the time machine before she could do so.
Once he had returned to the past, Wallabee contacted the KND and informed them of his past self's predicament. Future Numbuh 4 had then led Sector V to the school, defeated the Girl Squad, and rescued his younger self. Margie then attempted to contact her future self, but Numbuh 3 crushed her time machine in the same manner her granddaughter had done in the future, destroying Margie's last chance to skip justice and sealing Madam Margaret's and the Girl Squad's fate. The school was subsequently destroyed, and Margie was taken to Kids Next Door Arctic Base. 75 years later, on those same grounds, a playground was built for both boys and girls.
- Margie's future self, Madam Margaret, seems loosely based on the villain Granny Goodness from DC Comics.