Celestia. She's the 'Good Pony' in that story that pulls the sun.
If neither is acceptable, I could go with the less 'mythological' 'Mane' characters. They have magic powers that stem from the 'Elements of Harmony' which, when combined, make friendship. Each 'Mane' Pony represents one portion of the Elements,
Loyalty - Represented by Rainbow Dash
Honesty - Represented by Apple Jack
Generosity - Represented by Rarity
Kindness - Represented by Fluttershy
Laughter - Represented by Pinkie Pie
Magic - Represented by Twilight Sparkle
Edit:In case you couldn't tell, yes the title is Literal; Frienship IS magic.