Clara Schumann was on a concert tour in the spring of 1865. This card might have been for a visitor at a concert in Leipzig. The name does not appear in the correspondence with Johannes Brahms and not in the three volume Schumann biography by Berthold Litzmann --the two main sources for Clara Schumann's life after the death of Robert in 1856.
Scherer & Nabholtz. "Photograph of Clara Schumann." (1865) Digital version published by Brown Fine Arts Library, Fondren Library, Rice University: http://hdl.handle.net/1911/13027.
Schumann, Clara, 1819-1896--Portraits
Digital version published by Brown Fine Arts Library, Fondren Library, Rice University