Riko isn't aware that her mother is a Witchblade wielder. This is because Masane shows fear of her reaction when she found out. In episode 20, they get attacked by a monster at a bridge, giving her no choice but to transform. After the battle's over, Riko finally saw her in that state, but she just runs and hugs her. She isn't afraid of her in that state, she's still her mother.