If she’s a very good friend, can you go be with her? Otherwise, I’d get on the phone and take my cues from what she says. If she wants to rant at the drunk driver, gently join in. If she wants to cry, just listen and make soothing noises periodically. “Oh, sweetie. I know. It’s okay to cry. I love you. I’m here.” Repeat for as long as she’s crying. If you start crying, too, that’s okay. It might be just what she needs. She’s in a very dark place, and you can’t get her out because she’s right to be so sad. However, you can go be in the dark place with her so she’s not alone: https://youtu.be/1Evwgu369Jw.
I would try very hard not to offer advice. Maybe keep paper and a pen close by so you can jot down all the advice that pops into your head while you’re talking. When people are this sad, we want to give advice to make it all better. But she’s getting great advice all day long, and I bet she just can’t take it anymore. She knows she needs to eat, that it might be okay, that she has to sleep and trust the doctors.
During your conversation, she might say scary things. She might express that she has no idea how to continue her life if her daughter dies. You might get really nervous to hear that, so prepare yourself for this possibility and think about what to do if you get too anxious yourself. You can say you’ll be right back, you need to get the door or use the bathroom. You can take a sip of a warm beverage you’ve prepared for yourself. You can listen to your breathing or feel your feet as a grounding exercise. You can even just hold the phone away from your ear for a second, take a really deep breath, and look around to remind yourself that you are safe. In your friend’s situation, it’s normal to wonder how life could possibly go on. It doesn’t mean she will kill herself if her daughter dies, at all. And if she can tell you about these scary thoughts without judgment, there’s a good chance she’ll tell you, too, if she ever does seriously consider it.
I wonder if she’s lashing out because people are telling her it’ll be okay (that’s BS), or that she just needs to believe things will work out (that puts undue responsibility on the mother). People might also say things like “I can’t bear to see you so sad”. Anything that might read to her as “Stop being so sad.” or “Your sadness is making others uncomfortable.” will make her lash out, for sure.
It’s brave and kind of you to help.