Wikipedia Biographical Summary:

"...Mary Musselman Whitmer (August 27, 1778 - January 1856) was the wife of Peter Whitmer, Sr. Through her son David Whitmer, she and her family became acquainted with Joseph Smith, Jr. around 1828. In 1829, probably during June, she was caring for three boarders (Joseph Smith, Emma Hale Smith, and Oliver Cowdery) in addition to her large household while the Book of Mormon was being translated. She said she was often overloaded with work to the extent she felt it quite a burden. During this time, the male boarders and members of her household were speaking of being shown the Golden Plates. One evening when she went to milk the cows, she said that a stranger with a knapsack spoke to her, explained what was going on in her house, comforted her, then produced a bundle of plates from his knapsack, turned the leaves for her, showed her the engravings, exhorted her to faith in bearing her burden a little longer, then suddenly vanished with the plates. She always called the stranger Brother Nephi.

She was baptized a member of the Mormon Church by Oliver Cowdery in Seneca lake, April 18, 1830. She was the mother of five of the Witnesses to the Book of Mormon..."

SOURCE: http://en.wikipedia.org/wiki/Mary_Whitmer