Lilian Grace Ida Orpen was a daughter of Francis Henry Samuel Orpen* and his wife Sarah Anne, born Murray, and an older sister of Katherine (Kate) 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. Lilian collected a variety of natural history specimens for the South African Museum, Cape Town. Her contributions included a collection of small mammals, many of them very rare, with some birds, snakes, land molluscs and insects of various orders (1897); eleven mammals (some as skins, others in alcohol) and a Solifuga that was new to the museum's collection (1899); and some insects from Douglas (1904).
Lilian and Kate, 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. At some time Lilian also presented plant specimens to the McGregor Museum, as well as a manuscript titled "Christmas story" (1891). She and Katherine also presented the museum in 1941 with a collection of manuscripts relating to their grandfather, Charles E.H. Orpen (1791-1856).