It seems like Robin just wanted to traumatize Kiruko and it left her reeling so bad she was in a state where she was in shock, overwhelmed with her thoughts and was desperate to escape the noise in her mind. She just wanted the safe place that is Maru and seeing him, she completely snapped back to reality, untied herself and tried to stop Maru from kill someone after seeing her like that.
I wanted to see Maru punch his lights out. It’s a great scene showing Robin couldn’t escape or rile him up, but he didn’t get what he deserved for terrorizing Kiruko.