The cause was complications of Crohn’s disease, an incurable gastrointestinal disorder that she was found to have when she was 19, said her brother, Dr. Michael Jaff, a vascular medicine specialist.

Ms. Jaff was the founder and director of Advocacy for Patients With Chronic Illness, an organization she started in her home in 2005 after she found that she could no longer work at her law practice. She assisted more than 5,000 clients in filing claims with insurance companies so they could receive increased coverage of what she called invisible disabilities — among them Crohn’s disease, autoimmune disorders, congenital metabolic disorders, and sickle cell anemia.

But her mission went far beyond steering patients through the maze of the health insurance industry, in which, she argued, the providers do all they can to minimize coverage of chronic illness. She spoke to groups across the country, lobbied politicians, and published a handbook, ‘‘Know Your Rights,’’ which offers guidance on insurance appeals, Social Security disability benefits, job discrimination, educational equity, and housing discrimination.

Ms. Jaff wrote an amicus brief in National Federation of Independent Business v. Sebelius, the case in which the US Supreme Court in June upheld President Obama’s Affordable Care Act. Her brief argued in support of the provision prohibiting insurance companies from discriminating against people with existing conditions.

‘‘She has had an impact across the country,’’ said Victoria Veltri, who heads the Connecticut Office of the Healthcare Advocate, an independent state agency. ‘‘She was one of the people really involved in pushing that provision. She knew it was the key to ensuring that people with chronic illness finally would have access to health care that would prevent them from having to go into massive debt or bankruptcy.’’

After the Supreme Court ruling, Ms. Jaff told The Hartford Courant: ‘‘I live and breathe chronic-illness law, and in my estimation this is the most important civil rights advance for people with chronic illnesses ever. There can never be equality if we can’t get health insurance.’’