Her devastated mother Marie announced the news on Instagram, describing her "beautiful" daughter as "a bright shining star".
The talented singer, who performed with the girl group from 2002 to 2013, died yesterday morning, weeks after revealing the disease was terminal.
Marie said: "It's with deep heartbreak that I'm sharing the news that my beautiful daughter Sarah has sadly passed away. "She fought so strongly from her diagnosis until her last day. "She slipped away peacefully this morning.
I'd like to thank everyone for their kind support over the past year. It meant the world to Sarah, and it gave her great strength and comfort to know she was loved.Read more on msn.com