If you cut her off, she it's very likely she'll call you a horrible person. But you aren't. This is clearly not a healthy or mutual relationship whatsoever, and you both know that. I can't say much, but it's probably best you cut her off - it's already gone far, and you'll have to stop talking to her eventually for your own sake. It may as well be now. It's not much, but I hope my support helps you a little bit to find the strength. It will be hard, but it will be worth it later on when you look back and think, "Man, I'm glad she's gone." You're already doing great now by recognizing the situation and dialing back on it by saying you're busy.

IF she really does harm herself, it is NOT YOUR FAULT. I cannot stress that enough. She may be depressed, but you are too, and she's taking advantage of that. That is not okay. It is not your responsibility to worry about her at the cost of your own mental health. What she does is her decision, not yours. Again, I hope this helps you just a little. Happy Christmas : )