Looking at that girl there I would suggest that she didn't need to use her toe to pull the trigger. Her arms were long enough to do the job.
But if we argue that Sheila shot herself first with the silencer on and then carefully put it away in the box and then into the cupboard, then I must say I do not believe it. She would just have taken it off (if she were able to) and left it by her side. She didn't strike me as being a particularly tidy person?