Who was Moses' sister?

Answer: Miriam

Miriam the prophetess, Aaron's sister, led the women with tambourines; Numbers 26:59 names Aaron, Moses and their sister Miriam.

“Then Miriam the prophetess, Aaron’s sister, took a tambourine in her hand, and all the women followed her with tambourines and dancing. and Amram’s wife was named Jochebed. She was also a daughter of Levi, born to Levi in Egypt. To Amram she bore Aaron, Moses, and their sister Miriam.”— Exodus 15:20; Numbers 26:59 (BSB)