Sorry to take so long to respond. I've been involved in a job change and wasn't checking the board.
You're probably correct. From materials posted at Ancestry and elsewhere, it appears that Sarah was a daughter of Anthony and Grietje. "Sarah" may well be an Anglicized version of "Engeltje." Someone with more knowledge in linguistics may be able to address this.(Sarah would have been around 50 when Cornelia was born, if she's the mother.) I haven't seen an authority for Jan's marriage to Engeltje anywhere yet (just assertions that the marriage occurred around 1680) nor any authoritative death date for Sarah (just supposition that it had to occur before the "marriage" to Engeltje in 1680). David Kipp Conover (et al.; cf. conovergenealogy.com for starters) claim that Sarah died in 1715 in New York.