Well the truth is she is simply not engaged anymore. That is unless the person she is engaged to is interested in multiple sexual partners as well. Define the reason for being married?
Do you want to be married for a few years while everything is going fine. A fair weather marriage. Divorce is just a step away.
Your friend really has to review her reasons for getting engaged. Maybe this is a wake up call, in her heart she really does not want this man. She really is not interested in the bonds that make marriage the institution that it is in our society.
Perhaps it is a good thing and she has confronted her fears and is saving both her and her partner years of grief and un happiness.