If she gives you the impression that she would be ok talking about the call, as well as her thoughts and feelings surrounding it, offer her an open ear.
If not, don't force it. People need to make their own decisions for what is best for them. If she is ok talking about it with you, listening and simply being there for her can go a lot farther than people give it credit for. Being on tough calls is part of the job no doubt, and questioning yourself in the role is a good sign that you are still human. I wouldn't want to be treated by the medic for whom tough calls never happen. One of the things that she might find, if she is willing to talk, is that as she recounts the story, each time gets easier. There is less to hold inside and the story will flesh out many of the less-obvious details as she tells it repeatedly. Again, only if she is interested.
As for her time in medic school, that is moot if she is truly not meant for the job. In the end that may be what is best for her and for any of her future potential patients. Her process is what it will be. Being supportive and present for her is about some of the best stuff you can do for her. She may also want to reach out to more senior practitioners. I had a bad call once and reached out to my boss, my mom and dad, and other medics I respected a great deal.
Hope this helps.