Angela was born with a degenerative condition that would eventually cripple her for life. Her father Charles, a brilliant medical scientist and virologist, created the T-virus as a means to cure her condition. The virus worked, but needed to be kept in check with an antigen to prevent any spontaneous mutations. Thanks to T, Angela could walk without crutches, but Umbrella seized her father's research and used it to turn the T-virus into a biological weapon.
Resident Evil: Apocalypse
In Apocalypse, Angela hides out at her school while the T-virus ravages Raccoon City. She is found by Jill Valentine and a group of survivors who have been sent by her father to rescue her. Alice, a former Umbrella agent and guinea pig, senses the T-virus in her and looks inside the girl's lunchbox to find vials of the T-virus antidote.
When Alice and co. arrive at Raccoon City Hall to take an Umbrella chopper out of the doomed city, they are captured by Major Cain and his men. Cain shoots Angela's father to coerce Alice into fighting the mutant super-soldier Nemesis, but a firefight ensues and the creature turns on his handlers. The survivors manage to flee aboard the chopper before Raccoon City is obliterated by a nuclear missile, but the chopper crashes in the Arklay Mountains. Everyone but Alice escapes before Umbrella find them, and Angela uses her T-induced psionic connection with Alice to find her weeks later.
Resident Evil: Extinction
Angela makes no appearance in the third RE film and no explanation is given on-screen as to what happened to her. However, the novelisation of Extinction reveals that Alice and her friends are pursued by Umbrella as the T-virus begins sweeping the United States. In Detroit, Alice - who had unknowingly been implanted with a control device at the end of the last film - is taken control of by Dr. Sam Isaacs. Isaacs orders the brainwashed Alice to kill Angela, and Alice supposedly kills the girl by blasting her head off with a shotgun.