Who was Delphine's mother?

Your question refers to the 2003 novel by Louise Erdrich, The Master Butchers Singing Club. This story is about the separate lives of Delphine Watzka and her partner Cyprian, as well as Fidelis Waldvogel and his family. They all live in Argus, North Dakota. 

Throughout the story Delphine’s mother is unknown. All that is known is her father Roy Watzka, a severe alcholic. At the end of the book it is revealed that her biological mother is actually Mazarine Shimek’s mother (a close friend of Delphine’s), Mrs. Shimez. Step-and-a-Half, the town scrap collector, found her abandoned in an outhouse and gave her to Roy to raise.

But this book focuses on showing non-biological familial ties as well. So when answering your question, who is Delphine’s mother, it is also important to point out non-biological mothering figures in the text. Eva Waldvogel, who helps run the butcher shop, becomes a role model for Delphine. She teaches her many domestic and other skills that a mother traditionally would.

Erdrich, L. (2003). The Master Butchers Singing Club. New York: HarperCollinsPublishers.