Sheila was not strongly built. My wife always says that she did not have muscles in her arms. " Those were the days before people went to gyms . " Perhaps a little bit of an exageration but clearly a beautiful but slightly built woman.
She was also regarded as poorly coordinated and had not managed to learn to drive, as far as I know, in an age when most people, particularly in rural environments did. Sheila disliked guns and it is a myth to think that people brought up on farms naturally became competent or even familiar with handling weapons. As a farmer's daughter, my wife hasn't a clue how to shoot either. Let alone the forensic evidence, in my opinion it really does defy belief to think that Sheila could have shot her family and very brutally battered her tall, strong father in the way consistent with the very severe injuries which he sustained. She lacked the strength, coordination and competence to have been responsible.