In 2003, while on safari, Susan's husband was killed. Tommy survived, but the blood transfusion that saved Susan's life was tainted with HIV. Later on, she gave birth to her daughter, Lisa. She used to be a teacher, but when it was discovered Susan had HIV along with a complete refusal to take medication (being a devoted believer that HIV doesn't cause AIDS), the school paid her a large amount of money so she wouldn't sue the school for wrongful dismissal. She ended up becoming a stay-at-home mom.
Lisa died of pneumocystis pneumonia after Susan failed to provide her with any treatment when she got sick with a sore throat. Dr. Hutton did nothing to treat Lisa as well. While testifying in court, Susan collapsed, suffering from toxoplasmosis, which is a brain disease that people with AIDS gets. She dies from complications of it. It is later revealed that Susan was HIV-positive long before Lisa was born and later passed on the disease to her son, Tommy. (SVU: "Retro")