Canon for reference
Nuala was sent as a gift by Auberon and Titania to Dream of the Endless on a diplomatic mission to entreat Dream’s help in closing Hell. Nuala believed once her mission was over she’d return home, but truthfully no one believed the mission would succeed and when her brother Cluracan visited her he informed her that Titania would not accept rejection of the gift, whether or not Dream lent his assistance, and so Nuala would never be able to return home.