Once Ann Radcliffe retired from publishing, all kinds of rumors started to spread about her, including some that distressed her greatly. After she died, there was even more speculation.
Research:

Britannica, The Editors of Encyclopaedia. "Ann Radcliffe". Encyclopedia Britannica, 5 Jul. 2023, https://www.britannica.com/biography/Ann-Radcliffe-English-author
Radcliffe, Ann. “The Romance of the Forest, interspersed with some pieces of poetry.” London. 1824. Accessed online: https://www.gutenberg.org/cache/epub/64701/pg64701-images.html
Radcliffe, Ann. “Gaston de Blondeville: Or The Court of Henry III. Keeping Festival in Ardenne, a Romance. St. Alban's Abbey, a Metrical Tale: with Some Poetical Pieces, Volume 1.” H. Colburn. 1826. Accessed online: https://play.google.com/store/books/details?id=vi03AAAAIAAJ&rdid=book-vi03AAAAIAAJ&rdot=1
Radcliffe, Ann. “A Journey Made in the Summer of 1794, Through Holland and the Western Frontier of Germany, With a Return Down the Rhine: To Which Are Added Observations During a Tour to the Lakes of Lancashire, Westmoreland and Cumberland, in Two Volumes.” G.G. and Robinson. London. 1795. Accessed online: https://www.gutenberg.org/cache/epub/62795/pg62795-images.html
Facer, Ruth. “Ann Radcliffe (1764-1823).” Chawton House Library. 2012. http://www.chawtonhouse.org/wp-content/uploads/2012/06/Ann-Radcliffe.pdf
Dugdale, John. “Happy 250th, Ann Radcliffe.” The Guardian. Oct. 31, 2014. https://www.theguardian.com/books/2014/oct/31/ann-radcliffe-gothic-pioneer-snubbed-horace-walpole-the-castle-of-oronto-250-years-celebrations#:~:text=Another%20250th%20anniversary%2C%20of%20Ann,sent%20up%20in%20Northanger%20Abbey.
Flood, Allison. “Gothic fiction pioneer Ann Radcliffe may have been inspired by mother-in-law.” The Guardian. Jan. 30, 2014. https://www.theguardian.com/books/2014/jan/30/ann-radcliffe-gothic-fiction-mother-in-law
McIntyre, Clara Frances. “Anne Radcliffe in Relation to her Time.” Yale University Press. 1920. Accessed online: https://archive.org/details/annradcliffeinre00mcinuoft/page/n3/mode/2up
“Mr. Radcliffe … “ Sunday Dispatch/ London. October 30, 1825. https://www.newspapers.com/image/813446539/?terms=%22Ann%20Radcliffe%22&match=1
McKillop, Alan D. “Mrs. Radcliffe on the Supernatural in Poetry.” The Journal of English and Germanic Philology, vol. 31, no. 3, 1932, pp. 352–59. JSTOR. http://www.jstor.org/stable/27703650
Clarke, N. (2005). Anna Seward: Swan, Duckling or Goose?. In: Batchelor, J., Kaplan, C. (eds) British Women’s Writing in the Long Eighteenth Century. Palgrave Macmillan, London. https://doi.org/10.1057/9780230595972_3
Norton, Rictor. “Mistress of Udolpho.” Leicester University Press. 1999.
Thomas, Donald. “Queen of Terrors.” The Guardian. July 10, 1964. https://www.newspapers.com/image/259612656/?terms=%22Ann%20Radcliffe%22&match=1
Townshend, D., & Wright, A. (2014). Gothic and Romantic engagements The critical reception of Ann Radcliffe, 1789–1850. In D. Townshend & A. Wright (Eds.), Ann Radcliffe, Romanticism and the Gothic (pp. 3-32). Cambridge: Cambridge University Press. doi:10.1017/CBO9781139507448.003
Schwertfeger, S. 'No spoilers, please': the crux of illustrating the explained Gothic without explaining the mystery. Palgrave Commun3, 16 (2017). https://doi.org/10.1057/s41599-017-0018-z
Scott, Sir Walter. “The Lives of the Novelists.” London. 1906. Accessed online: https://play.google.com/store/books/details?id=DXPPAAAAMAAJ&rdid=book-DXPPAAAAMAAJ&rdot=1
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