Actually, the harpsicord played in the little parlor at Mount Vernon probably belonged to Washington's step-granddaughter, Nelly Custis.  The instrument was a gift from the President to 14 year old Nelly around 1793 and was delivered from London retailer Longman and Broderip.  By all accounts it was a top-of-the-line harpsicord acquired as the piano was just coming into popularity.  It was an extensively modified double keyboard harpsichord containing a complex plucking mechanism utilizing leather plectra rather than quill, a set of knobs and pedals which operated stops, and a Venetian swell. All allowed the user to play more expressively giving this particular harpsichord a mellower sound well suited to the changing demands of compositions of the period.  According to conservators and music historians, these innovations made this particular harpsichord different from any other surviving period harpsichord in the US. 
    Eventually Nelly's harpsichord moved to Washington's Mount Vernon in 1797 at the end of his second term, and except for a short stay at the home of Nelly's brother, remained there in its original condition until 2016 when curators determined that the environment in that old mansion was not good for the preservation of the instrument.  Mount Vernon called John Watson who is, as it happens, a builder of harpsichords.  They commissioned him to build a playable replica which would become part of the Mount Vernon exhibit.  And so the project was begun in Watson's workshop using the original instrument, now housed in more friendly climes in Williamsburg, as a model for the building of the replica.  This year and in 2020, Mr. Washington's harpsichord will once again be played in his home to better depict the important role of music in the late 18th century American experience.  See how John Watson made the replica here and see the fascinating history of Nelly's harpsichord  here..  Both are worthy of your time.  We'll never know whether this replica sounds the same as the original harpsichord.  Watson believes it will be close.