Family #48 in the 1834 Grimm census.
Family #50 in the 1857 Grimm census.
Family #483 in the 1897 Grimm census.
Christina was born after the 1798 census and married before the 1834 census. This means she was not captured in a census with her biological parents. Unless we find a descendant who has detailed private records or gain access to the right church records, we will probably never know her last name at birth.
Studying the maternal haplogroup of Christina's female descendants could help narrow down her maternal ancestry.
Head of the Household Gotlieb Hepp, age 39 in 1816, deceased 1824
Wife Katharina Margaretha Hepp, age 62
Child #1 Gottlieb Hepp, age 26
Wife of Child #1 Christina Hepp, age 29
Grandchild #1 Anna Regina Hepp, age 9 years 6 months
Grandchild #2 Margaretha Hepp, age 7
Grandchild #3 Heinrich Hepp, age 1 year 6 months
Grandchild #4 Johann Friedrich Stehl, age 3, stepson of his son Gottlieb
Brother Johannes Hepp, age 30 in 1816, to household #33
The comment about Johann Friedrich Stehl suggests that the child belongs to Gottfried's daughter-in-law, Christina, most likely from a marriage prior to Gottlieb Hepp. The problem is that the child is 3 years old, and Gottlieb the son and Christina have a child of their own who is under 2. Does this mean that his wife had another man's child was she was married to Gottlieb? If the answer is no, then:
His current wife, Christina, can be the mother of only the youngest child, Heinrich Hepp.
Gottlieb the son must have been married previously to produce the two older children, ages 10 and 7.
If Gottlieb is only 26, then his first marriage would have been when he was 15, which is on the young side, even for Volga Germans during that time frame.
It's possible the census takers made a clerical error, but his age in the 1834 census matches his age in the 1857 census, so one would have to believe the error was carried through two different censuses.
Gottlieb could have been married previously to a widow with two daughters, and she passed away by 1831, leaving Gottlieb the only guardian for the girls. Then when he remarried, his wife Christina brought her son Johann Friedrich Stehl into the family. Although neither of the girls were biologically Gottlieb's, they were not entered into the 1834 census as his step-daughters.
The only way to clarify what the situation was is by looking for birth and marriage records for all involved. Those records have not yet been translated and are not available to the general public.
Wife of Child #1 Katharina Margaretha Hepp, age 23
Grandchild #1 Katharina Charlotta Hepp, age 2
Grandchild #2 Jakob Friedrich Hepp, age 1 year 3 months
Child #2 Katharina Elisabeth Hepp, age 20
Child #3 Barbara Hepp, age 16
Child #4 Christina Elisabeth Hepp, age 13
Step-Son Georg Friedrich Stähle, age 26
Wife of Step-Son Katharina Barbara Stähle, age 27
Grandchild #3 Eva Katharina Stähle, age 4
Grandchild #4 Alexander Stähle, age 2
Grandchild #5 Friedrich Stähle, age 1
Grandchild #6 Christian Jakob Stähle, age 3 months
She is not listed in the 1897 Grimm census with the rest of her family members.
She most likely passed away by that year. Had she survived, he would have been 92 years old.
↑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 15, family #48.
↑1857 Census of Grimm in the District of Saratov, Russia, dated 5 November 1857; Translated by Brent Mai, Concordia University, Portland, Oregon; Published by Dynasty Publishing, Beaverton, OR, USA; Published 2005; page 19, family #50.
↑1897 Grimm (Lesnoi Karamysh), Russia Census List, Translated by Richard Rye, Compiled and Edited by John Groh, Contributor Henry Schmick; American Historical Society of Germans from Russia, Lincoln, Nebraska, USA; Published 2017; page 118, family #483.