Get ready for Callan or another IDI to say that Patsy could have seen the heart, not while JB was alive..but, later...after John had brought her up. So, lets nip that in the bud right now....JB was covered when Patsy came into the room, and even if she wasn't...I am quite positive that she wouldn't have been staring at her daughter's hand, and the "well drawn little heart", while her daughter's dead body layed on the floor. She would have been too distraught to even notice her hands, much less...think to herself (as she said in her interview)....what a well drawn little heart it was. The MAIN thing though is....that JB's body was covered up when Patsy entered the room, so she couldn't have seen it then.
My guess is that she denied seeing it, to point to YET ANOTHER thing that the "intruder" did. If not, then she could have said, that she saw it as she was tucking her into bed that night, or something.