As with most of the Flock's parents, the identity of Fang's mother was never revealed.
In The Angel Experiment, Angel, while telling the Flock what she'd learned about their origins, explained to Fang that his mother was a teenager who was told that he had died. After the rest of the Flock fell asleep, Fang told Max that he speculated his mother was a crack addict. In School's Out - Forever, Max says that Fang's mother gave him up for adoption.
They are not able to follow any lads, and in Saving the World and Other Extreme Sports, Jeb says that most of the information they found was probably planted, casting doubt on any of their theories about Fang's mother.
She appeared in a photo in Max Ride: First Flight.