"When I heard about Lisa's plight, my heart broke," Rihanna told the magazine. "I said, `I need to get the word out about Lisa right away."'
Flynn is a 41-year-old mother of two young children. She was diagnosed in November with acute myelogenous leukemia, a fast-growing cancer of the blood and bone marrow. Doctors have told her she has four to six weeks to find a suitable donor, according to People.
Flynn said she was stunned by the singer's efforts on her behalf.
"For Rihanna to even be thinking about helping others and putting herself out there when she is so busy with her career is tremendous," Flynn said.
Rihanna, born Robyn Rihanna Fenty, was named an honorary cultural ambassador for her native Caribbean island on Thursday. Earlier this month, she and Jay-Z won a Grammy in the rap/sung collaboration category, for her hit "Umbrella."