In The Life and Works of Annie Louisa Swynnerton by Susan Thomson (Warrington, Manchester Art Press, 2018, p39), there is an oil sketch reproduced – a preparatory work for the Equestrian portrait of Lady Mercy Greville. The original is held at the Tate Britain, London. I’ve included the sketch on the web page for that portrait.
ANNIE LOUISA SWYNNERTON (1844-1933) 