During the shower scene, of course, she was stabbed multiple times, front and back. After Norman-as-his-mother leaves, cut back to her. She is shown leaning against the shower wall, and as she slowly slides down the wall, no blood marks are visible. I know that the scene was purposely shot so as not to show blood during the stabbing montage, but its too incredulous to believe that no blood would be left on the wall as she slides down.