Anna Massey Lea Merritt (September 13, 1844-April 7, 1930) was an American painter and printmaker active in Great Britain.
Biography on Wikipedia: https://en.wikipedia.org/wiki/Anna_Lea_Merritt

Portrait of Sir William Boxall, R.A. by Anna Lea Merritt
c.1870s / Oil on canvas / 49″x36″ / Royal Academy of Arts, London, UK

Anna Lea Merritt on The British Museum site: https://www.britishmuseum.org/collection/term/BIOG38200

Further reading:
https://nmwa.org/art/artists/anna-lea-merritt/
https://artuk.org/discover/artists/merritt-anna-lea-18441930
https://www.annexgalleries.com/artists/biography/2708/Merritt/Anna