Helen Keller is famous for being a tremendously successful deaf, blind and mute writer and activist. She is also central to one of the most famous cases of cryptomnesia, a circumstance when a person utilizes implicit information whilst experiencing no phenomenal familiarity with the content. In this case, Helen wrote the story The Frost King and was accused of plagiarizing The Frost Fairies by Margaret Canby.
In the history of analytic philosophy, there is much debate about whether a cryptomnesic experience counts as a memory. Bertrand Russell  thought that a real memory needed the bearer to have the sense of familiarity that it was indeed a memory. His thinking is certainly shared by Hume , who argued that memories, as opposed to imaginings, were particularly vivid to the person experiencing them. Martin and Deutscher  pointed out that the necessary conditions of a memory were not the phenomenal experience of it as a memory, but the correct causal connection to the perceptual event that precipitated it. Contemporary cognitive science echos Martin and Deutscher's observation. It recognizes a variety of memory systems, some of which may be active during cryptomnesia and some--such as conscious familiarity--may be passive, making any binary classification of Helen Keller's experience insufficient to capture the complex cognitive processes occurring in her mind at the time she wrote her story.
Philosophical issues aside, here is a great video of Helen and her teacher Anne Sullivan:
Thanks to tomble for the link.
 Russell, B. Analysis of Mind
 Martin. C.B. & Deutscher M. (1966) Remembering. The Philosophical Review. 75(2). 161-196