She just became an honorary cultural ambassador for Barbados, and now Rihanna is advocating for another cause: a New York City leukemia patient in urgent need of a bone marrow donor.

The 20-year-old singer is working with DKMS, an international donor network based in Tubingen, Germany, to try to find a donor for Lisa Gershowitz Flynn, People magazine reported on its Web site Saturday.

"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."