Sorry for a late reply.
When I read your post the main thing I took from it was that it reads that your wife is being affected by depression.
I didn’t really fully understand depression and what it can do. From my understanding and experience its maybe responsible and definitely one of the biggest factors in almost everything you describe.
Ignoring covid and lock-in…because lets face it they have been ridiculous .. everyone has had problems.
Your biggest priority is that 6yo. Helping your wife get out of that bad place feels like the only way forward. I would definitely spend ages reading up on depression, there are really big DO’s and DON’Ts (there are quite a few DON’Ts in your post) and then you probably need to prepare yourself for many months of really patient and winding your neck in. If it doesn’t work, at least you’ll always know you did the right thing
Remember people in depression think and say things that they wouldn’t normally think. Its like a different personality. Best example I read is “what do you think someone is thinking about when they are drowning”
best of luck.