From the mid-19th century onwards religious orders for women developed within the "high" portion of the Anglican Church. Their activities were centered on community work - especially social work, teaching, and nursing. There were also lay sisters who were not formal members of the order. In several Oliphant novels, women looking for meaning in their lives are attracted to these sisterhoods. As Agnes says in Carità, "I wanted to do something more, to do some duty in the world, not to be like a vegetable in the garden." This theme is generally part of a subplot, not the major story line of the novel.
Three of these five novels refer to an organized religious order as described above. Regarding the other two novels: in The Perpetual Curate there is an unofficial sisterhood of two (or possibly more) women under the sponsorship of their Curate, wearing modest grey cloaks as a sort of uniform while doing social work in the poor area of town. In Whiteladies there is actually no real sisterhood, but rather a single individual who has appointed herself a sort of nun, doing penance for the "sins" of her forebears who had taken over the confiscated lands of a priory.