RIHANNA HELPS FIND MARROW TRANSPLANT

It's been a busy week for Rihanna, but when the Grammy-winning singer learned about a leukemia-stricken New York City mom of two who desperately needs a marrow transplant, she immediately stepped forward to help.

"When I heard about Lisa [Gershowitz Flynn]'s plight, my heart broke," Rihanna says. "I said, ‘I need to get the word out about Lisa right away.' " The sultry 20-year-old singer returned to her native Barbados, where she has been named an honorary cultural ambassador. Specifically, Rihanna is working with DKMS – the world's largest non-profit marrow donor center to help raise awareness for the need for people to come forward to become donors.

"I think DKMS is an incredible charity because you can really see the results," says Rihanna, who performed at the DKMS Linked Against Leukemia gala last May for free. She adds: "My own charity, Believe, works specifically with children in need [and with children with leukemia]. Children need their mothers more than anything else in the world. Lisa has two children. My charity will continue to work with DKMS, because in finding a way to save Lisa's life, we will in turn be saving her children's lives."

Flynn, 41, is blown away that Rihanna is taking time to try to find a donor match for her and countless others who may die if they don't get one.

"For Rihanna to even be thinking about helping others and putting herself out there when she is so busy with her career is tremendous," says Flynn, the mother of Michael, 5, and Alexandra, 3, who learned she has an aggressive form of cancer called Acute Myelogenous Leukemia the day after Thanksgiving. Doctors told her she has four to six weeks to find a life-saving donor match.