Hamer was a voting rights activist and civil rights leader, instrumental in organizing Mississippi Freedom Summer for the Student Nonviolent Coordinating Committee (SNCC), and later became the Vice-Chair of the Mississippi Freedom Democratic Party.
She was known for her electrifying oratory presence, and relentless pursuit of civil rights for all.
Woodard didn't say if she'll be playing Hamer in the 4-hour film, but my guess is she likely will be, although obviously in her later life. Hamer died on March 14, 1977 at age 59.
However, she could also very well just be producing it, with some other actress (or actresses) starring.
Here's the interview: