Albert Barnes Commentary Exodus 15:20

"And Miriam the prophetess, the sister of Aaron, took a timbrel in her hand; and all the women went out after her with timbrels and with dances." — Exodus 15:20 (ASV)

And Miriam the prophetess — The part assigned here to Miriam and the women of Israel is in accordance with both Egyptian and Hebrew customs. The men are represented as singing the hymn in chorus, under the guidance of Moses; at each interval, Miriam and the women sang the refrain, marking time with the timbrel and with the measured, rhythmical movements always associated with solemn festivities (2 Samuel 6:5, and marginal references). The word used in this passage for the timbrel is Egyptian. Judging from its etymology and the figures depicted with it in the inscriptions, it was probably the round instrument.

Miriam is called a prophetess, evidently (Numbers 12:2) because she and Aaron had received divine communications. The word is used here in its proper sense of uttering words suggested by the Spirit of God . She is called the sister of Aaron, most probably to indicate her special position as coordinate, not with Moses the leader of the nation, but with his chief aid and instrument.