Sounds like she desperately needs help, and I would please urge you never to ignore someone who is suicidal regardless of whether you consider the threat to be just that. It’s usually the people that make the threat that carry it out because it is on their mind alot.
Does she have a dual diagnosis worker in the community? What drugs is she taking? Where is she living at the moment?
I can imagine that you’re at the end of your tether and that the anger is helping you to cope, however there really is no way to detach from this because she is your daughter.
You can access support from here and Al Anon, also practice lots of self care for YOU.
Police can do welfare checks if you’re worried but also can assess her mental health by a doctor at the station. Please don’t think because she makes threats she wouldn’t carry it out. In her own way she is suffering immensely.