Jena, calling the police was never going to be a waste of time. Even if NOTHING is done as a result - there is now a paper trail. You notified the cops. If they don't bring her home, it is not your fault.
Taking her to the emergency room (or whatever it is called) - it is highly likely you would get there and she would say, "Mum made it all up, I'm fine," and they would have to discharge her. But time would have been wasted FOR HER. Other people's time wasted too (including yours) but right now, think in terms of inconvenience for her. It's time to make life darned inconvenient, and to hit her with natural consequences. And the natural consequences for making suicide threats - you get to be evaluated and that often means a lot of waiting around. Take your knitting.
It also is more documentation.
Go through her life. Look at the basics you MUST provide - shelter, food, clothing - and strip it back to basics. She has to earn back ANY privileges. You might not be able to physically stop her going AWOL, but until she toes the line, then under your roof she gets a mattress on the floor, steamed rice to eat and basic op-shop clothing to wear. Everything else - put it into storage somewhere. Hopefully it shouldn't take long.
I do agree that drugs need to be considered, but I don't think they're the main issue here. She's behaving badly all on her own, I suspect. I'm still flabbergasted by her writing "deceased" on that bill and sending it back. That's not drugs, that's pure mischief. Hang on - isn't that a Federal offence? Tampering with someone else's mail? If it is, check it out then read her the riot act. Tell her that you are within your rights to report it and ask for charges to be pressed. It was a blasted stupid thing to do - did she think it wouldn't ever come back to bite her? and certainly shows extreme immaturity. She does not at the moment deserve any adult pleasures or choices. She blew those options right out of the water.
You really could have done without all this. But since it is what has happened - use your anger. I've got some steel-capped Lotte Lenya boots you can borrow (they not only have steel caps, but when you click the heels together, poisoned blades pop out of the toes). Get kicking!
Marg