How much do you need Steve?
If I recall correctly she had participated in a shoot in Scotland and had asked to fire a gun, which she did with David Boutflour steadying her hand. It was a one-off incident. The murder weapon itself was stiff, suggesting not only the difficulty in reloading twice (as well as changing the magazine), but probably chipping or doing some damage to her nails, which did not occur.
Of course to suggest Sheila as the perpetrator is just a smokescreen to distract from the real culprit: a man who had learned to shoot as a boy on the farm as well as at a school known for its cadet force, a stepping stone to an army career.