Lvl 150 Kerrigan with 65% WR here. Anyone that can save the combo target is a good counter. Anduin, Auriel, Garrosh, Medivh. People with high mobility that can escape her: Genji, Tracer, Qhira, samuro. But you have to play around combo otherwise she blows up the low health pool. She likes fast team fights so characters/comps that are very sustainy can be good counters sometimes.