It seems that Elizabeth Jonker was my 2nd great grand aunt (her parents were my g-g-g-grandparents).
I believe Elizabeth's mother was named Cornelia Frederika Stein, born 24 Dec 1822 in Kampen, Overijssel province, Netherlands, and her father was Hilbert Hendriks Jonker, born Dec 1815 in Meppel, Drenthe province, Netherlands.
I believe that Cornelia's mother was Sijmetje Thomasdr van Rijn, born 5 Mar 1792 in Noordwijck, Zuid-Holland province, Netherlands, and her father was Heinrich August Stein, born 28 Oct 1755 in Stuttgart, Württemberg. They married in Kampen, Overijssel, Netherlands, on 21 Jul 1815 (when he was 59 and she was 23 - presumably an interesting story there of some sort).
I have only the names of Elizabeth's paternal grandparents: Hendrik Jonker and Aafjen Hilberts Maas. On the marriage entry for Cornelia and Hilbert, the only information given about them is that Hendrik was a "Schipper" (captain of some sort of boat or ship) and Aafjen was without occupation. Given their names, it's probably fairly safe to assume they were both Dutch.