I know her father was Jan Jensen, he named daughter Gertrude wife of Paul Kuster (Kerster) in his will. But who was her mother?

Conventional wisdom says she was born in 1726. But is that right? What seems like well researched work on the Kuster/Custer family says that Paul and Gertrude married about 1759 and had children including Abraham in 1774 and possibly a son even later than that. Not bad for a lady born in 1726!

I believe most credible research on this family says that Paul Custer who married Gertrude Jensen was the son of Hermanus. But there are dissenting voices. As would be expected, all of the sons of Paulus Kuster named a son after him so there were multiple Paul Kusters in the third generation and as is typical of amateur genealogists, figuring out which was which is beyond their skills. That is not to say I have figured it out either. It’s just my judgement that the versions of this family’s history that show it the way I am showing it seem better researched to my eye.

I would really like to know when Paul Kuster was born as it would help establish a reasonable range as to when Gertrude was born but the fact that all these people were Mennonites works against things here -- remember Mennonites, like other anabaptists, believed in adult baptism, not child baptism. Consequently, whereas for most of our German Reformed ancestors, the church minister typically felt a responsibility to record all the baptisms he performed (with some exceptions) -- there seem to be no similar Mennonite records.