Here and in Melachim I, 15:2, it says that Asa's mother was Ma'achah. Above (13:2) it says that she was Aviyah's mother!
Radak #1: Really, she was the mother of Asa's father Aviyah. Verses often call the father's father 'father', e.g. "El Re'u'el Avihem" (Shemos 2:18), and also the father's mother is called mother. "Em Asa" is like Em Aviv. Malbim #1 - his grandmother was called his mother, because she raised him.
Radak #2, Malbim #2: Perhaps also Asa's mother was named Ma'achah bas Avshalom.
Why does it mention what his mother did?
Radak: Even though his [mother or] grandmother was a Rasha, he was not drawn after her.
What is "Miflatzes"?
'Rashi', Rashi Melachim I, 13:3, from Avodah Zarah 44a: It was MaFLi LeiTZanuSah (a wondrous mockery). She made the form of a male organ for the idol, and had 'Bi'ah' with it every day.
Refer to Melachim I, 15:13 3:2
