One of the earliest reported possible female serial killers was the Chinese Queen Ji Xia. She was reported to of been the wife of Xia of Chen and probably from the state Zheng. The Xia Dynasty was ca 2070-1600 BC. The Queen was suspected of killing 3 husbands, a son as well as a ruler.
[Lisa Ann Raphals, Sharing the Light: Representations of Women and Virtue in Early China, SUNY press, 1998, p. 67, ancient source cited Zuo, Zhao 28.2, pp. 1492-3.]