I show the parents of Peter Probasco who married Martha Probasco as Hendrick Probasco & Elstje Covenhoven per the baptismal record:
Six Mile Run Dutch Reformed Church Baptisms, Somerset County, NJ Baptism: 23 Dec 1759 Perbesco, Hendrik and Elsje--Pieter
The last name for Elstje was listed in The Van Kouwenhoven-Conover Family by Lincoln C. Cocheu. It could have been her maiden name, or even from a previous marriage. I have not found any more info on this.