It is a judge's duty to confront deep-seated psychological and personal issues when a crime as extreme as this was was committed. This to my knowledge was NEVER done as I don't expect Sheila's notes saw daylight during the trial. It was easier to point a finger at Jeremy.
Sheila's background as well as Jeremy's should have been studied to see if there'd been an indicator of her erratic behaviour and the circumstances which brought about her mental health issues because they don't happen overnight. There was far more evidence to Sheila's uncertain and unbalanced background than there is to Jeremy's. The law is an ass and it's so unfair.