She dedicated almost a decade to the meticulous research and writing that culminated in her final book Thicker than Water: Siblings and their Relations, 1780-1920, published by Oxford late in 2012 just before her 80th birthday. This pioneering study is yet to receive its full recognition. Leonore demonstrates the significance of sibling relationships and their key role in the extensive family networks that provided the capital, personnel, skills and contracts crucial to the rapidly expanding commercial and professional enterprises of the era, and how these changed as families became smaller from the end of the 19th century. Through studies of particular families (including the Freuds, Gladstones, Wedgwoods and Darwins), she explored sibling intimacy and incest, and some famous brother-sister relationships.