I believe Dr Ferguson or whoever it was originally diagnosed Sheila with psychosis and paranoia, and then later decided on paranoid schizophrenia.
So apart from the schizophrenia muddling her thoughts and disconnecting her from reality, Sheila thought that everyone was out to get her, even the twins! This threat alone may have caused Sheila to take drastic action if she feared for her life, who knows?
Anyway, in Sheila's case, I dont think it would have been as simple as taking her medicine for a guaranteed status quo regarding her well being, April!
Certainly, in the grip of psychosis, Sheila's thoughts would have been muddled. However once on meds, she'd have been clearer, which was probably one of the reasons she stopped taking them, ie she thought she was better, ergo, no need for medication. Incidentally, this is probably why most schizophrenics stop taking oral meds. Ultimately, not taking them led to Sheila's second breakdown and return to hospital. During that stay it was decided that the best way forward was meds by injection.
Schizophrenics will never be 'cured'. However, with medication, the condition, along with the muddled thoughts which lead to psychosis, can be controlled. What you have gone to great pains to have us believe, Sheila's belief that "everyone, including the twins, was out to get her" didn't form part of the reasons for her second admission. This being verified by Dr Ferguson. Not that I think you'll be prepared to listen to any of what I've said because you're too determined to make Sheila responsible, at whatever cost to her reputation!