Over the whole period “between 12 and 19 per cent [of those whose letters survive] wrote all their own letters …. the number of women for who there is evidence of their actually writing letters rose from 50 per cent in the 1540s to some 79 per cent by the end of the 16th century … the proportion of women for whom no holograph letters survive fell from 28 per cent in the first decade of the period to an estimated 17 per cent by the years 1600 to 1609.” (p. 96)
From Women Letter-Writers in Tudor England, James Daybell, OUP 2006 (found today on the “new books” shelf at the London Library – which can be a really treasure.)
An nice example, Elizabeth Bourne, “wife of Anthony, the son of John Bourne, Mary I’s principal secretary of state”. Some 70 of her letters survive, written in holograph in several different hands. She also wrote original poetry and sometimes used the pseudonyms Frances Wesley and Anne Hayes, which she called her “secrete syphers”.
A search of the web and electronic academic database returned nothing on her – one more for the literary collection.