No need to apologise- i prefer bluntness to beating around the bush.
I work in a similar area to you, but not a secure unit (although it can be locked if required). My area is overdoses and suicide attempts - our worst cases are transferred to secure psychiatric units like yours. So, yes i agree and can see exactly where you're coming from in terms of range and scope of mental illness. Most of mine are experiencing crises, they live in the community, are generally well supported and managed from the MH teams. But, I treat the suicide attempts - hangings, gassings, self harmers and overdoses (NAC and naloxone infusions generally).
In saying that I've had my fair share of 'difficult' patients - obviously limited in terms of confidentiality. But, i've looked after several high profile murderers - one who'd murdered an elderly lady to steal a ring. Another was a serial killer, the less said about him the better. There was a lady years ago who murdered several members of her family. Recently I had a person who was trying to poison my city with a nerve agent, with a plan to kill and cut up his community psych team. Allegedly, he'd been honing his dissection skills on small mammals he'd bought online. There was no bed for him in a secure unit so he stayed with us for 4 days, with constant security presence as he made threats to several staff members.
I don't see a mental health crisis occurring with ET. I believe she had insight into what she was doing, and as far as I can tell she's using her mental health background as an excuse to lessen the severity of her involvement. She obviously has mental health issues, but she was warm and loving to her own children. I genuinely believe she didn't like Arthur (for whatever reason) and wanted him gone from her life.