Lady of the Haystack
made her appearance in 1776 at Bourton, near Bristol. She was young and beautiful, graceful, and evidently accustomed to good society. She lived for four years in a haystack; but was ultimately kept by Mrs. Hannah More in an asylum, and died suddenly in December, 1801. Mrs. More called her Louisa; but she was probably a Mademoiselle La Frülen, natural daughter of Francis Joseph I., Emperor of Austria.
(See World of Wonders, p. 134.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894