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. Over 40 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 eight titles: The Magnetic North, The Open Question, The Messenger, Votes for Women, Under the Southern Cross, The Convert, Come and Find Me, My Little Sister.
Also note the listed works by Elizabeth Robins at A Celebration of Women Writers. Most Robins texts from this index link to the HathiTrust repository of public domain works.
Google books yields many titles, but makes it difficult to distinguish between Elizabeth Robins and Elizabeth Robins Pennell, a different writer.