She is Michael and Lincoln's mother. Michael took her maiden name because she told him his father was an abusive drunk, whereas Lincoln maintained Aldo's name surname. Michael also named a boat 'Christina Rose' in memory of his mother. Christina was believed to be deceased until Season 4 Episode 16 - The Sunshine State where it's revealed that she is not only alive, but in possession of Scylla. It is also revealed that she once worked for The Company.