In this AU, Moondancer has Sunburst’s role from the main continuity.

After Twilight was sent away, Moondancer was alone and constantly studied in hopes of getting to the same school Twilight was sent to. Unfortunately, even with her getting her cutie mark, her magical prowess wasn’t enough to get into the school. She knew countless spells but her magic wasn’t strong enough to actually be able to do them.

She and Twilight would later be reunited and Moondancer would realize that, even if her magic wasn’t that strong, she still could use the knowledge she’s learned over the years to help others.

I tried to go with Moondancer’s hairstyle from gen 1 here, since the gen 4 design is just a Twilight palette swap.