Wife of Child #1 Maria Magdalena Zerber Rau, age 23
Grandchild #1 Nikolaus Rau, age 3
Grandchild #2 Anna Katharina Rau, age 6 months
Child #2 Nikolaus Rau, age 27
Wife of Child #2 Maria Barbara Schmück Rau, age 24
Grandchild #3 Anna Elisabeth Rau, age 6 months
Child #3 Johann Georg Peter Rau, age 25
Wife of Child #3 Anna Barbara Schröder Rau, age 20
Child #4 Johann Georg Rau, age 20
Child #5 Konrad Rau, age 7
Child #6 Anna Elisabeth Rau, age 14
Child #7 Maria Magdalena Rau, age 12
Child #8 Anna Margaretha Rau, age 10
In the 1834 Grimm census, her son Nikolaus Rau is listed as Jakob Polst's step son. From this we can infer that her first husband, Johannes Rau, passed away at some point before 1816, giving her enough time to remarry and then become a widow for a second time when Jakob Polst died in 1816.
The census does not confirm when she died; it also does not say that Jakob Polst was a widower prior to his death.
It's possible that Maria Magdalena remarried after the death of Jakob Polst in 1816 and that she was still living in 1834. If she survived to 1834, she would have been 58 years old. It's also possible that she was deceased.
Head of the Household Jakob Polst, age 41 in 1816, deceased 1816
Child #1 Nikolaus Rau, age 38, step-son
Wife of Child #1 Katharina Rau, age 36, stepson's wife
Grandchild #1 Maria Katharina Rau, age 12 years 6 months
Grandchild #2 Katharina Margaretha Rau, age 9 years 6 months
Grandchild #3 Elisabeth Rau, age 9 years 6 months
Grandchild #4 Charlotta Rau, age 8
Grandchild #5 Charlotta Rau, age 5
Grandchild #6 Katharina Barbara Rau, age 6 weeks
↑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, Nebraska, USA; Published date: 1995; family #130 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 53, family #177, Jakob Polst family.