All you can do is listen and validate how she feels. When she's ranting, just say "I'm sorry you feel that way" and then change the subject or walk away. Do not continue to engage in arguments or her baiting tactics.
NC is actually for you. It is to help you get grounded and focus on you and what you need to do to survive. Always remember, you did not break her, therefore you can't fix her.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
