Previously, Hanssens lead the development of Lambda Legal Defense and Education Fund's HIV litigation and policy work as the AIDS project director for eight years. During her earlier work with the AIDS Law Project of Pennsylvania, Hanssens created and managed a model on-site legal assistance program for single parents with HIV in Philadelphia-area hospitals and clinics that brought together legal, medical and social services.
While working for the New Jersey Department of the Public Advocate in the 1980s, she successfully litigated the state's first case addressing involuntary HIV testing, a system-wide challenge to the segregation and treatment of prisoners with HIV, and the only federal appeals court decision recognizing the right of incarcerated women to funded elective abortions.
Her legislative lawyering has ranged from work on Pennsylvania's standby guardianship law to proposed legislation for comprehensive prevention programming in prisons and revisions to state HIV confidentiality and testing laws. She also has been a visiting clinical professor and the director of the Women and AIDS Clinic at Rutgers University Law School-Newark, and regularly writes and conducts trainings on HIV legal issues.