It had seemed like a good idea at the time, until Sunset actually read what Twilight wrote in her letter. She'd already said yes to seeing Celestia again, and she wouldn't go back on her word. As long as she remained convinced that this was a good idea and that it would all end well, she could get through it without a problem.
6/21/2016: Now with cover art designed by the very generous Novel-Idea! Thank you so much!