You can not force her into mental illness help. Taking a horse to water you know and all. You can request couples counseling.

Only a court order can force her into treatment.

You can tell her you WILL move out and leave her unless she immediately gets help for whatever is causing her to be hateful , mean and very abusive. She has threatened harm.., that is a big line to cross.

If you had a daughter? Sister ? Mother? Etc in this situation what would you advise them to do ??