Jordin Sparks Remembers Sister Who Died of Sickle Cell Complications: 'She Was So Strong'

Last week, the American Idol winner’s 16-year-old step-sister Bryanna Jackson-Frias died following complications from her lifelong battle with sickle cell anemia.

The disease, which is more common in people of African descent, causes red blood cells to stick to vessel walls, blocking blood flow and preventing oxygen from reaching tissues; the lack of oxygen can damage organs and cause pain so severe it requires hospitalization.

“She fought her entire life — all 16 years, in and out of hospitals. And she was so strong,” Sparks, 28, told PEOPLE Now exclusively on Wednesday. “She just dealt with it, you know, and there was never a complaint. I’m sure she had moments where she was like, ‘Okay, this hurts,’ but she was one of the strongest people that I’ve ever encountered.”