It seems impossible that she is not connected to either Balthasar Rau or Konrad Rau, both in the 1775 Grimm census, but I can't find a link. She must have been born in another village and moved to Grimm as an adult.
Head of the Household Georg Dumler, age 49 in 1816, deceased 1817
Wife Margaretha Barbara [Rau] Dumler, age 65
Child #1 Johann Philipp Dumler, age 37
Wife of Child #1 Christina [Bürkheim] Dumler, age 36
Grandchild #1 Katharina Margaretha Dumler, age 15
Grandchild #2 Barbara Dumler, age 14
Grandchild #3 Johann Philipp Dumler, age 11
Grandchild #4 Christina Margaretha Dumler, age 8
Grandchild #5 Katharina Elisabeth Dumler, age 6
Grandchild #6 Elisabeth Margaretha Dumler, age 4 years 9 months
Grandchild #7 Margaretha Barbara Dumler, age 2 years 6 months
Child #2 Johann Georg Dumler, age 16 in 1816, to household #148
Child #3 Johann Jakob Dumler, age 14 in 1816, to household #4
Child #4 Friedrich Dumler, age 10 in 1816, to household #148
Child #5 Johann Michael Dumler, age 4 years 3 months in 1816, to household #291
↑The 1775 and 1798 Census of the German Colony on the Volga, Lesnoy Karamysh, also known as Grimm; Published by the American Historical Society of Germans from Russia, Lincoln, NE, USA; Published 1995; family #82 in the 1798 census.
↑1834 Census of Grimm in the District of Saratov, Russia, dated 2 February 1835. Translated by Brent Mai, Concordia University, Portland, Oregon; Published by Dynasty Publishing, Beaverton, OR, USA; Published 2011; page 47, family #150.