Consider, how old were you when she was still patting your butt. Pubescent? That is incest. Did she touch you and lean on you and get between you and your girl friend when you were having a conversation at the dinner table or the living room.
Did she flash you? Spread her legs so you could see her sex particularly with no panties. If these are your experiences (as they are mine) your mother did act on her incestuos relationship with you.
Of course my mother also had me strip naked for pictures by her friend the photograher when I was 12. I assume if your mother had done that you would definately call it incest.