Guess I should have finished looking, before I posted my other message:
1920 Cook Cty., IL Census, Enumer. Dist. #279, Sheet 2A, 2719 W. 39th Street: Erdmann, Minnie (53-Widow), Wanda (14- daughter). States she was born in Germany, immigrated in 1880 and naturalized in 1898. Minnie was a dressmaker.
I would check into naturalization records for 1898 in Cook County, IL- for Emil and Minnie.
In 1930, Victor, MN there is a Minnie Erdmann (63 yrs- widow) living with Herman Erdmann, listed as a sister. Both born in Germany.
Good Luck,
Susan