The Open Question (1898)
Come and Find Me (1907-8)
The Mills of the Gods (published 1908)
My Little Sister (1913)
Off site, the best source for finding books by Elizabeth Robins in the public domain is at Open Library. 33 works are listed with eleven available as e-book, including The Magnetic North, The Convert, The Open Question, My Little Sister, Come and Find Me, Under the Southern Cross, A Dark Lantern, Way Stations (non-fiction), Votes for Women (play), The Messenger, Camilla.
Project Gutenberg lists seven titles: The Magnetic North, The Open Question, The Messenger, Votes for Women, Under the Southern Cross, The Convert, My Little Sister.
Also note the author's listed works at A Celebration of Women Writers. Google books yields many titles, but makes it difficult to distinguish between Elizabeth Robins and Elizabeth Robins Pennell, a different writer.