So I kind of see the lady in the black dress as Kyuubey but also as the grief of the girl in the white dress, which whispers to her what she most desires and tempts her into making a contract with Kyuubey, then as she progresses on as a magical girl, the grief slowly starts gaining more and more control over her until finally, the story of this poor girl meets its end as her soul gem is taken over by darkness and becomes a grief seed. ....Did I get it right~?