A couple weeks ago we rented the movie The Other Boleyn Girl. Since I don't know much about Ann Boleyn - and had never heard of her sister - I went to the library and checked out "Ann Boleyn, A Biography" by Marie Louise Bruce. I can't find a link to the book on-line. It was published in 1972 and seems to be out of print.
I enjoyed both book (excellent and informative) and movie (Hollywood brain rot but enough to get me interested in the real Ann Boleyn). Of course the movie took great liberties with the facts of Mary's and Ann's lives. Historical movies usually tell more about the period in which they're produced than they do about the period the story is supposed to cover.
Ann Boleyn was an extraordinary person, both in the movie and in life; and the real Mary Boleyn was - well, let's just say - not the girl in the movie.
Note on the usual, gratuitous, anti-Christian cheap-shot required in all standard Hollywood productions: According to Bruce, Ann was not charged with witchcraft, and witchcraft was not a felony in England in 1536. The charges of Treason and conspiring to kill the King were quite enough to have her condemned. It's typical whoever made the movie thought it necessary to add a new charge to Queen Ann's indictment.