My cousin passed away in her 30's a few yrs after diagnosed with adult stills disease. read it's like ra, what could have made her pass away?

Sorry for your loss: Still's disease sets up a severe inflammatory response. Worse case - this causes the sac around the heart to become irritated and can lead to heartbeat irregularity. Rarely, the lungs can become irritated and cause a fluid shift resulting in difficulty breathing. The disease is not considered to be an inherited kind - rather a rare side effect from a viral infection. Prayers for you & family.