#48 in the 1834 census.
According to the 1834 census, Margaretha's "mother" Christina had a son, Johann Friedrich Stehl, who was three years old in 1834. If Margaretha was seven years old, then Christina could not have been her mother. Her father Gottlieb Hepp must have been married at least once before he married Christina, and that first wife must have been Margaretha's mother.
Unfortunately Margaretha's mother was born after the 1798 census and died before the 1834 census, so her name was never captured in an official record. At least not one yet identified. Interim census records only captured male names, not female names. Studying the maternal haplogroup of Anna Dorothea's female descendants could help narrow down her maternal ancestry.
1834 Grimm Census 
Note that the inclusion of Christina Hepp's child by her first husband indicates that Christina was not the biological mother of the two oldest children, Anna Regina and her sister Margaretha, since they were older than Johann Friedrich Stehl. Youngest child, Heinrich Hepp, would have been Margaretha's step brother, since neither child had a common parent.
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