Roelfke (Julia) Wendt was born Roelofje Meeuw, daughter of Dirk Roelfs Meeuw and Grietje Derks Zwart. Mom Grietje died in 1838, and dad remarried in 1842 to Geertruida van Hoek.
I couldn't find a passenger list on them, nor any mention in a USA census, but this is definitely the right family. Both dad Dirk and step mom Geertruida (Gertrude) are buried in the same cemetery as Roelfke (Julia), and their dates of birth are correct.
Here are the details on the family:
Dirk Roelf Meeuw, day laborer Born isle of Borkum (Germany) 09 May 1801 at 23.00 hrs Died USA 03 May 1879 Buried Trinity Lutheran cemetery, Dillon, Marshall County, Iowa Son of Roelof Esderds Meeuw and Tetjen Jansen de Jonge
Marriage 1) Married Uithuizen (province of Groningen) 24 Aug 1833 to: Grietje Derks Zwart / Swart Born Warffum 05 Mar 1811 Died isle of Texel 01 July 1838 Daughter of Eeke / IJke Derks Vloo, father NN
Marriage: https://familysearch.org/pal:/MM9.3.1/TH-1-15694-23162-33?cc=2026219&wc=M9QQ-DYY:n1837874907 right hand page, rest of document on next image
Death Grietje Derks/IJkes Zwart/Swart https://familysearch.org/pal:/MM9.3.1/TH-1-9782-29436-14?cc=2020117&wc=M9QW-265:n1573673886
Children: 1. Tetje Meeuw (female) Born Uithuizen 20 Mar 1833 https://familysearch.org/pal:/MM9.3.1/TH-1-15696-34923-19?cc=2026219&wc=M9QQ-DPP:1837471706
2. Roelofje Meeuw (female) Born isle of Texel July 31 July 1837 https://familysearch.org/pal:/MM9.3.1/TH-1-9781-47223-46?cc=1831469&wc=10742452
Marriage 2) Married isle of Texel 19 May 1842 to: Geertruida van Hoek Born Wybelsum (Germany) 01 Feb 1813 Died USA 09 Nov 1895 Buried Trinity Lutheran cemetery, Dillon, Marshall County, Iowa Daughter of Klaas Sippen van Hoek and Anke Freerks