The name Stefani is a girl's name of German origin. Stefani and discussed in our forums with posts like "Adding Then Eliminating -- Girls Themed".
From the experts:
Germans spell Stephanie with an f though the i ending is not traditional. Lady Gaga dropped the Stefani and No Doubt's Gwen sports is as a surname. Despite the celebrity connections, we say if you want to name your daughter Stephanie, name her Stephanie.