Biological mother of Sephiroth.
Lucrecia is the biological mother of our Lord Sephiroth, who allowed her unborn son to be injected with the cells of Jenova. She was, obviously, a passionate scientist, or perhaps simply passionate about Professor Hojo, and willing to do anything he asked of her.... although that's highly unlikely, considering the love interest of Vincent Valentine.
During pregnancy, Lucrecia began having dreams, or visions of the horrors her unborn son would one day commit, and in an untimely encounter, discovered Vincent shot by Hojo. Fearing for his life, Lucrecia then exposed him to the stagnated mako, causing the being known as Chaos to be absorbed into his body. Though his life was saved, he was left in a feral madness.
Disgusted with all that she had done to those she cared about and the changes Jenova's cells had wrought in her own body, she attempted to commit suicide. However, she was unable to easily die because of the presence of Jenova's cells in her body, and, thus, she isolated herself in a cave and trapped herself within mako crystals. During the events of Final Fantasy VII, she is discovered by Vincent and the others, and she asks if Sephiroth had died yet. Vincent, hoping to help her rest in peace, falsely tells her that he had.