Do you mean directly? With her own two hands? No one. Cersei leaves direct murders to peons. Indirectly - she is responsible for the death of Ned Stark, Robb, Bran and Sansa's father. She ordered Jaime to kill Bran Stark - only by a miracle the boy lived. She also had me framed for murder along with my father ...I was saved by a guilty Jaime and the grace of the Gods.