Katherine Irene Theodora ("Kate") Orpen was a daughter of Francis Hnry Samuel Orpen* and his wife Sarah Anne, born Murray, and a younger sister of Lilian G.I. Orpen*. She appears to have lived on her father's farm "St Clair", on the banks of the Vaal River near Douglas, for most of her life. One of her activities was writing poetry, but she also collected plants and prehistoric artefacts. It seems that she began collecting plants in 1897, when she presented Albany Museum, Grahamstown, with a single plant that was new to its collection, and sent her first specimens to P. MacOwan* at the Government Herbarium in Cape Town. Her donations to the Government Herbarium continued for some years and included rare succulents, dried plants and seeds collected near Prieska (1898), and plants from the northern parts of the magisterial district of Herbert (around Douglas, Griqualand West) in 1902. Later she sent specimens also to the Royal Botanical Gardens at Kew, near London. Her specimens are preserved in the Compton Herbarium in Cape Town, and at Kew.
Kate and her sister Lilian, identified as "the misses Orpen of Douglas", presented a collection of bored and grooved stones, bone tools and stone artefacts from Uniondale and Moorreesburg to the South African Museum, Cape Town, in 1906. Three years later Miss K. Orpen, Miss L. Orpen and Mr C.E.H. Orpen (their elder brother, 1856-1910) presented stone artefacts to the McGregor Museum in Kimberley.