Can a daughter perform Matru Navami Shradh for her deceased mother, or must it be a son?

A daughter can absolutely perform Matru Navami Shradh for her deceased mother. While the Dharmashastra tradition historically assigned Shradh performance to sons, the texts also recognize that daughters may perform Shradh when no son is available, and several traditions (especially in Bengal and South India) specifically encourage daughters’ participation. The sincere love and devotion of a daughter for her mother is no less spiritually powerful than a son’s.