Miriam is the older sister of Moses; she’s also the sister of Aaron, but we don’t know which one is older.
At the time Moses is born, there’s a degree to kill all baby boys. His mom hides him as long as she can, then she puts him in a basket and places him in the Nile River. Mariam watches at a distance to see what happens. When the pharaoh’s daughter finds him, Miriam pops up and offers to find a woman to nurse him; she picks her mom.
As an adult, Miriam is a prophet and worship leader of sorts, leading the women in song and dance to celebrate God’s rescue when they crossed the sea to escape the Egyptians.
Unfortunately, what we know most about Miriam is when she and Aaron oppose Moses over his choice for a wife and out of jealousy. God’s judgment is quick, instantly inflicting her with leprosy (a contagious skin disease, untreatable at the time). Though Aaron is also at fault, he is not so afflicted, suggesting that perhaps Mariam led their tiny rebellion. When Aaron sees what happens to his sister, he immediately admits his bad attitude and begs Moses to intervene. Moses does and implicitly God heals her. The whole nation then waits for her for seven days as prescribed by Jewish law.
A few years later Miriam dies; there’s no mention of the people mourning her death, a sad end to a promising life.
Though Mariam started well as a brave and obedient daughter and later as a prophet and worship leader, she let judgment and jealousy define her later life. God was not pleased.
[Read Miriam’s main story in Numbers 12:1-15.]