Moonwatcher I am so sorry that you’re still going through this. My comment is so so incredibly long, wow. My apologies for that, I don’t know what happened! 
This is just my opinion but after reading your recent posting/comment I have to say that your daughter appears to enjoy keeping you at the end of her string, having the ability to yank on a string with you being tossed around at the other end. She also enjoys letting go of that string to let you feel the lack of her presence, wondering where she has gone. Once she feels you have suffered from her absence she then grabs that string and pulls, causing you to suddenly be yanked around like a rag doll.
This precarious position you are placed in is not healthy. You must remove this string from her grasp, you have to be unyankable. When she sends you a text she knows you are on the other end either weeping or desperately hoping for normalcy. I know it may be very hard but I don’t see any other way towards a solution, so I would suggest blocking your daughter on your phone for a period of time (a week, two weeks, maybe just three days) only after texting her to let her know that she can’t expect you to be there to chat after routinely berating you, and that you won’t stand for it anymore either. Then block her. You may be thinking “but what if she needs me?” You may also feel guilty for preventing her from contacting you. All that I understand, you obviously love her as she is your daughter. However, you can’t keep on like this any longer. She will survive despite not being able to text or phone you, she is an adult and certainly does not need to have a 24/7 open line of communication with her mother in order to stay alive. Plus you are not a doctor or a psychiatrist nor are you her doctor or her psychiatrist, those are who she should seek help from, not her mother in the form of some voodoo doll. And while she may make poor decisions but you couldn’t stop that anyhow. (I only say the above because I can imagine you or anyone really trying to convince themselves why temporarily preventing communication would be cruel, and wanted you to know that that is not so. Here it is necessary in order for your relationship to improve and heal.)
If the above of much to difficult to digest I just thought of something similar. And this really depends on what type of phone you have but you should silence your daughters calls and texts so that you do not receive a notification when she contacts you. Some phone types you can send someone’s texts to a separate folder, others you can only go to their contact and enable “hide notifications”. This is different from blocking in that the messages she sends won’t be deleted in their entirety. So with her notifications hidden, make the conscious choice to only check your messages from her one day of the week. Pick one day where you sit down and devote 10 minutes or so to reading and or listening to all the messages she has sent you in that given week, and then dedicate the next 5 minutes to crafting a single very short response to her messages, via text. Your message should avoid all of the details and drama that her texts and whatnot no doubt contained, keep it short and sweet. Something like “hello daughter, I’ve just got caught up on your messages. I’m so sorry you are going through such a difficult time. I love you very much and hope you are well. - Mom”. Just something to let her know you are still there for her but on your terms only. Right now she has set all of the terms for your relationship with her, but now it’s time for you to take charge.
When you are no longer constantly available and willing to take her abuse, she may be forced to look at herself and see what she has done wrong. That will likely take a long time though so you mustn’t waiver. And when you no longer allow yourself to be on the receiving end of her wrath you will realize what it feels like to be a respected human again. Right now she gets to have her cake and eat it too. She gets to have her mother in her life while also blaming you and fighting with you for everything wrong in her life. Show her she can’t have it both ways, because no one should put up with this sort of treatment.
Please don’t allow yourself to be treated this way anymore. Just because she is going through a tough time does not mean you must also do the same, so please please please take care of yourself. Don’t wait any longer for her to change, take yourself out of the equation. Make sure you are doing some self care as well to keep you at your best.