Starwen has a collection task that the player can complete by showing her a Golden Feather and NOT giving her the said item.
When being shown a Golden Feather and not giving it to her, the player will receive Royal Note, which can be used to enter the castle premises and reach a pillar that increases your mana regeneration when activated.
Starwen can be found in the Midtown library, inside of the Witches' Guild.
Unlike Tess, Demlin, and Sennia, being friends with Starwen won't let you enter her house. She'll give a tip instead about how to acquire Magic Dust. This can be triggered by giving her Magic Dust after the Royal Note has been obtained.