The ill-fated mountaineer George Mallory's only book was "Boswell the Biographer"?
Henrietta de Maleprade-VisscherBorn 1715
Married (1745) to Lieut-Gen. Jacques Elie de Maleprade (b. 1693 or 1720). They had at least one daughter, Hillegonda Susanna de Maleprade (1746-1814).
This is probably the Madame Maleprade mentioned by Boswell.
Life with Boswell:
Boswell planned to see a Madame Maleprader on December 12, 1763. She was one of the ladies on the list given to him by the Countess of Nassau Beverweerd.
I follow the tentative identification in Boswell in Holland, which does, however, only supply her name and husband.