What is it that makes her not want to apply? The extra hours? Fear of the unknown? She really likes what she does now and doesn't like managing people?
Some reasons are more valid than others. You can listen supportively as she talks it out.
If she gets the job and hates it, what's plan B? Could she go back to her current job? Could she move to a new company? Could she retire sooner? Could she transfer to a different department?
If she applies and doesn't get the job, how will she feel? What will she do if she ends up with a terrible manager, whether she applies or not?
Sometimes thinking through all the options shows you don't have as much to lose as you think. It seems the security and comfortable situation are already lost, so there's not as much downside to giving a new position a try.