A 21-year-old female was hospitalized with recurrent lower limb purpura, epistaxis, and menorrhagia for 1 year. Laboratory tests: hemoglobin (Hb) 82 g/L, white blood cell (WBC) count 4.2×10<sup>9</sup>/L, platelets (PLT) 26×10<sup>9</sup>/L, reticulocytes 0.16 (16%), direct Coombs test (+), indirect Coombs test (-), antinuclear antibody (ANA) (-). Bone marrow examination showed marked hyperplasia, erythroid series accounted for 0.56 (56%), and 123 megakaryocytes per whole slide, mostly granular type. The most likely diagnosis is: