Sheila's mental health and it's possible affect on Sheila if she was responsible, is a very tricky subject really, even more so for me as it's one that I have absolutely no knowledge of, so I will not pretend to.
However, as far as I can see, there is nothing which indicates that her mental health had any effect on her actions that night. I understand that statistics, profiling and previous similar cases, may indicate a possibility that a certain action was caused by her illness, but it does not indicate that it did happen.
So with that in mind, we have to revert back to evidence, which is an ongoing endless debate, on this forum at least.
Although don't get me wrong, I do understand exactly where you are coming from and heck, you never know, you might be spot on, maybe that's exactly what did happen, but I also think that even if evidence did surface which indicates that Sheila was responsible, any theories about her mental health being the cause, would still remain just that, a theory, a good theory, maybe even a probable theory, but a theory none the less.
Obviously from the prosecution side of things, the mental health seed was sown by a guilty Jeremy trying to frame his adopted sister, as was his leaving a loaded rifle out in an easily accessible location. If that was the case then we don't know where the rifle was left at all, my personal opinion is that the whole rabbit shooting incident was made up.
I've rambled a bit there, but hopefully it still makes sense. 
Hi Hartley, welcome back, I admire your post.
But, Is it not a theory that JB walked approximately 4 miles in a wetsuit, entered the house through a window, picked up the gun, murdered his family, made it look like his sister, faked a call to himself, got out through a window, grabbed his mother bike and peddled all the way home through the fields, got showered at home, rang the police at Whitham, rang JM and told her all went well, rang the police at Chelmsford saying he had a call from his father, met the police at WHF and, was calm for 4 hours?
The other theory is...Sheila who had a mental condition, hated her mother, hated WHF, had been told by Colin that he had another woman, was told to take a holiday, was told she might be better living closer to home, picked up a gun in anger, shot her family, then killed herself. Sorry for using her illness, but it has to be considered. I could go on but I find it unfair.......
