Mobile Suit Gundam
Milly is the younger sister of Zeon spy Miharu Ratokie. When Kai decides to leave White Base, Miharu invites him to her home where he meets Milly and Jill. When she decides to sneak aboard White Base, Miharu provides Jill and Milly with money so they can eat, and says goodbye to them.
Mobile Suit Gundam: The Origin
In Mobile Suit Gundam: The Origin Artesia 0083, Sayla mentions that since Jill and Milly both refused to go to an orphanage, preferring to wait in their home for the return of their sister, Sayla's foundation will look out for them.