Family #7 in the 1767 Grimm census.
Family #66 in the 1798 Grimm census.
Anna Catharina Seibel/Seippell was born 13 September 1749 in Kaichen, Oberhessen, Hesse-Darmstadt, to parents Johann Adam Seippell and Anna Eva Kirchner.
Birth Record 
In searching for the family in immigration records, the only clue I had was her father's name from the 1767 Grimm census, where the name of her father and two siblings is recorded. I first assumed that Adam Seippell/Seibel perished on the journey to the Volga River region of Russia. His name cannot be found in List of Colonists to Russia in 1766, "Reports by Ivan Kulberg," nor in Deutsche Kolonisten auf dem Weg von St. Petersburg nach Saratow, Transportlisten von 1766-1767.  
I next searched for every possible iteration of the surname, which turned up widow Eva Selb. I believe that surname is either misspelled, modified, or abbreviated from the original form of Seibel. She was already a widow when she and her children embarked on their journey to Russia. She is the one who probably perished on the journey to to Volga, not her husband, who had died in Germany before the family left the country. But when identifying orphans, Russian record keepers apparently used their father's name, not their mother's name or the name of the most recently living parent.
As you can see from the Anna Katharina's birth record, her mother Eva's last name at birth was Kirchner. In the 1767 Grimm census, her children are listed immediately following immigrant Peter Kirchner.  Eva Seibel and Peter Kirchner were from the same town in Germany. Peter and Eva were most likely siblings or possibly cousins, immigrating together to Russia. Eva may have felt safer traveling with her brother and his wife, along with other people from the Friedberg area of what is now Germany. The entry for Eva and her children looks like this:
Listed three names above hers in the Kulberg Reports is her brother:
Also listed on the two open pages, 166-167, of the Kulberg Reports in close proximity to Eva's name are 11 other families who ended up in Grimm, Russia. These families include:
These things taken together show that Katharina and her husband NIkolaus Heimburch didn't randomly end up in Grimm, nor were the children they took in unknown orphans; they were her youngest siblings. They went to a village where there were others they knew from Germany, which probably helped soften the blow of losing her mother on the journey to the Volga.
By the time of the 1767 Grimm census, daughter Catharina/Katharina had married Nikolaus Heimbuch, a man who also traveled with the Seibels from Lübeck to St. Petersberg, arriving on 22 July 1766. If they didn't know each other before the journey to Russia, they certainly met on the boat and knew each other while they lived in Oranienbaum for the winter. The exact location of their marriage cannot yet be confirmed, but the couple was married by the time of the first census taken in Grimm in August of 1767.
1767 Grimm Census 
You can see from this entry that the "family" listed after Nikolaus and Katharina Heimbuch were orphans Nicholas Seibel, age 13, and Eva Seibel, age 11. These names and ages are in sync with the names in the Kulberg Reports on page 166.  Older brothers Johann and Adam were young enough and strong enough to survive the journey, but if they did, they did not settle in Grimm. The fact that the two youngest children were called orphans suggests that they had no living parents. For this reason, I believe their mother perished on the journey to the Volga.
For some reason, Katharina and her husband are not listed in the 1775 Grimm census, but they are back again in the 1798 Grimm census. The fact that their name was omitted seems to be an error on the part of the census takers.
1798 Grimm Census 
By 1834, neither Katharina nor her husband Nikolaus are listed with the rest of the family in the census.  Their son Nikolaus was the head of the household and he lived with one son, his wife, and two grandchildren. Most likely Katharina's husband Nikolaus passed away prior to 1816, and his death was included in that male-only census. Katharina's death could have taken place any anytime between the 1798 and 1834 censuses. The only way to confirm her death date would be through death records from the Grimm Lutheran church. Those records are currently not translated and are not available to the general public.
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