Who was the sister of Moses and Aaron?

The sister of Moses and Aaron was Miriam.

Miriam appears in the Exodus tradition as the daughter of Amram and Jochebed and the older sister of Moses and Aaron. When Moses is placed in a basket among the reeds of the Nile, his sister watches from a distance and helps arrange for their mother to nurse him after Pharaoh’s daughter discovers the child.

Later, Miriam is explicitly called a prophetess. After the Israelites escape from Pharaoh’s army, she leads the women with tambourines and dancing in a victory song beside the sea. The biblical tradition therefore presents her as more than a family member: she is one of the leaders associated with the Exodus.

Miriam and Aaron later challenge Moses over his authority and his marriage, and Miriam is temporarily afflicted with a skin disease before being restored to the camp. She dies at Kadesh in the wilderness. She is sometimes confused with Mary, the mother of Jesus, but they are different figures with different historical and biblical settings.