Help with boundry statagies

Hi, I need some advice or strategies to cope with my 20 year old daughter. She has been diagnosed with anxiety and depression a little while ago. She was on anti depressants but decided she didn't want to be on them anymore. I can not get her back to the drs. She makes erratic decisions and then expects me to clean up after her. I find it very hard to say no to her, there's a mothers guilt and also the emotional blackmail or cutting herself or suicide (which I'm scared will become a reality). She wants me at her beck and call 24/7 and we end up arguing if I am at work/sleeping/doing something that I can't answer her as soon as she calls (some mornings i wake up to 50 or 60 missed calls and then abusive texts). Explaning does nothing, she is irrational. Her father won't talk to her any more she does the same to him, she has only me and I'm scared if i stop she will have no one, but I think I'm also enabling her and I need to set boundries.....any suggestions with strategies are welcome. I'm at my wits end. Thank you 😊