equestriennen.
Etymology: pseudo-French feminine of equestrian adj. and n.
society > travel > transport > riding on horse (or other animal) > rider > [noun] > female rider
1864 in
1888 G. C. Boase Ducrow in XVI. 97/1 A well-known equestrienne.
This entry has not yet been fully updated (first published 1891; most recently modified version published online March 2018).