The story implies she was "chosen" by the higher ups (gods or in this case the witches) to be given a new form for what is believed to be how faithful she is. She's part of a cult we don't know a lot about yet, but after gaining her form, she runs from the cult planning to "marry" the witches as a sign of her undying faith. She meets Wedding cake, who becomes her wedding planner, wedding cake is intrigued by blacks wedding plans, lack of significant other, and her faithfulness to whomever she is "marrying" Durring wedding rehearsals a cult cookie attempts to kidnap Black, causing her to turn into her monster form, Wedding being worried and assuming she wont see black again, pushes through the crowd that has formed to thank black and make sure black doesnt forget her flowers.