> I recently came across a reference (below) to a woman joining the sisters of the Templars and I was wondering if anyone knows more about such a sisterhood
J. M. Upton-Ward, The Rule of the Templars (Woodbridge 1992) p. 36 paragraph 70 (translated from the Primitive Rule of the order, apparently predating your example):".... Henceforth, let not ladies be admitted as sisters into the house of the Temple ..."
U-W then gives a reference to A. Forey, Women and the Military Orders in the Twelft and Thirteenth Centuries, in: Studia Monastica 1987, pp. 63-92, with examples for the Templars on pp. 65s.