What's up with Lisa Trevor? What's her story?

Lisa Trevor is the daughter of George Trevor, the architect that built the Spencer mansion. Later on, Ozwell Spencer, the founder of Umbrella and owner of the mansion, invites Trevor and his family to spend a weekend there. It's actually a trap. The family are to become test subjects for the Arklay scientists.

George Trevor is infected with the T-Virus and is imprisoned beneath the mansion in a maze created for that purpose by Spencer. As a zombie, George is suppose to die from hunger there. However, once he loses consciousness he transforms into a new creature. He becomes the first of the Crimson Heads. He is then captured and after some tests, he is sealed away in a crypt behind the mansion.

Jessica Trevor, Lisa's mother dies after some experiments are performed on her. But Lisa for some reason manages to survive similar tests. She remains an Umbrella guinea pig for the next twenty-eight years.

You can also learn a lot more about Lisa by finding a translated copy of Wesker's Report 2.