Information on Mirabehn (or
Madeleine Slade, her original name) is readily available. Because she was such an important figure in Gandhi's life, all of the respected English language Gandhi biographies (single and multi-volume) discuss Mirabehn and her relationship with Gandhi.
I would not begin to give a biographical account of Mirabehn's life here, except to explain briefly how she came to Gandhi. In part, this was through Romain Rolland, who had written about both Beethoven, in whom she was deeply
interested, and Gandhi. The two met, and Rolland encouraged her to travel. After she bought a copy of Rolland's 1923 biography of Gandhi ("Mahatma Gandhi: The Man Who Became One With The Universal Being"), her destination was India and Gandhi. She arrived
there in November 1925.
Some of the works in which you might be interested are: two publications by Mirabehn - "Gleanings Gathered at Bapu's Feet", and "New and Old Gleanings", both published by
Navajivan Publishing House, Ahmedabad in 1949; Mirabehn's autobiography, "The Spirit's Pilgrimage", published by Longmans, London, 1960 (obviously the definitive work on her life); "Women Behind Mahatma Gandhi" by Eleanor Morton, Max Reinhardt, London, 1954; and "In Search of Gandhi" by Richard Attenborough, The Bodley Head, London, 1982.
I mention this last book because in it Attenborough recalls his visit to Mirabehn at her home near Vienna in
1973. Mirabehn died in her 90th year, on 20 July 1982. She did see the film before she died and, generally, approved of it.