Dreams are often gateways into our innermost feelings, emotions, and memories.
Starlight, since becoming Twilight's pupil, has been experiencing dreadfunightmares from memories she had previously been able to supress through her "Equality Movement" and determination to get revenge on Twilight Sparkle for taking away her "Perfect Town".
Using her dream powers, Princess Luna helps Starlight Glimmer cope with her past so she can move on without shame, remorse, or pain from past events.
ART BY: skitterpone
http://www.furaffinity.net/view/20714887/