The queen mother was the leading lady of the realm, usually holding the position for life. When she died, the title went to the mother of the next in line for the throne. There is no evidence that the queen mother had official duties, but she had significant influence.
Asherah is well known from Canaanite stories as the wife of the god El and the mother of seventy children, including Baal. Her image likely had noticeable sexual features, which was common in Canaanite art.
his grandmother: Literally his mother. The term “mother” can refer to any female ancestor. See 2 Chronicles 11:20, where Maacah is named as the mother of Abijah (Asa’s father).