Thank you all so much for your continuing words of support in this wild thread... it means the whole world to me!

The situation is just strange. Hikari, I'm just like you: I can't give up on people. Even my parents, who abused me for so many years, I didn't give up on them until it was clear that they had given up on me. And maybe not even then. I still tried to call my dad on Father's Day, left a message wishing him well, knowing they wouldn't pick up or call me back. I was right, and it hurts like hell. Why did I hurt myself by trying?
So last night was weird. I told my friend I didn't want to be friends and she hung up like I knew she would. Then she called me back and screamed in my ear for ten straight minutes while I yelled at her to stop because of how much she was hurting me. She told me she didn't care about anyone right now, not her mom, not her husband, not her only other friend (who talks to her about once every six months at this point), and not me either. She said that whatever she has going on right now, she feels like she's a "bowl of aggression" and hatred and has even lost the ability to cry. Her head was hurting worse than ever before in her life and despite not being sick, she had a 102 temperature.
When I finally got her to calm down and stop screaming without taking a breath, I told her that she was wrong when she said I didn't care. I'm more convinced than ever that she has the start of MS, and meds will level her out. I also told her that one of my best friends of 17 years has MS and I was upset thinking that I'd watch another friend suffer through it. In return, she finally told me why she stopped communicating with anyone this past week: it wasn't because of grad school so much, but because she's been screaming at every single person in her entire life (even strangers) and she wanted to save me from that. She screamed at her mom when her mom called yesterday, and she calls her mom the most important person in her life.
Three times during the conversation, she stopped in the middle of what she was saying, completely forgot what she wanted to say, and also forgot what she'd just said. She also tried to remember a single event from the day and couldn't remember anything fully. Whatever is happening with her is very scary, but she has the MRI this coming Tuesday and finds out the results next Thursday.
In the meantime, I'm giving her the space that she needs, because she wants to seal herself away from everyone right now. From what I heard last night, I completely understand why.
And for the record, "bad friend" means something different in Russian than in English... it's not great, but it's not an insult either. Still, I told her that regardless of what it means in Russian, I don't speak Russian and the term hurt me very badly. She promised to stop saying it to me.
So now it's a waiting game. I didn't permanently sever contact, but I'm not contacting her again until she feels she can communicate. We both agreed to this.