Opie published this novel anonymously. Paula Feldman first established it as her work based on the evidence of a letter to Sir John Gurney quoted by Garside (Peter Garside, James Raven, and Rainer Schöwerling. The English Novel 1770–1829: A Bibliographical Survey of Prose Fiction Published in the British Isles, 2 vols (Oxford: OUP, 2000); vol. 2: 1800–29 [1821:61]) in which she discusses anonymous publication. This evidence is confirmed by a letter requesting copies of her books as a gift for Madame Genlis (Huntington).
The Only Child; or, Portia Bellenden. London: J. Ebers, 1821.
The Only Child; or Portia Bellenden. Ed. Roxanne Eberle. Women and Romanticism. vol. 4. 1821. London: Routledge, 2006.