From Halopedia, the Halo wiki
Mrs. Leandro was Serin Osman's teacher in St. Malo. Because Serin was neglected by her junkie mother, Mrs. Leandro took care of her and brought her food in class. When Serin was abducted in 2517, Leandro reported her missing and later feared she had died. She continued to live in Cascade, which was left unscathed during the Human-Covenant War.
In 2553, she was shocked to see Serin on her doorway. She burst into tears and embraced Osman, happy to see that she was alive and well. She invited Osman into her home and the two began catching up on the last thirty-five years.
List of appearances