Barring any new evidence, that seems to be the only "smoking gun" reference at the moment that Neeltgen Meinderts who married into the s'Gravendijk family was the daughter of Meijndert Claesz. 

again, that's only proof that Pieter Jacobsz was married to Neeltgen Meijnderts...

if you want more records of her existance, https://www.erfgoedleiden.nl/collecties/archieven/archievenoverzicht/inventaris/memorixscan/eadid/0907A/inventarisnr/6289/afbeelding/NL-LdnRAL_AR_907A_6289_62  where Pieter is a widower. ONA Noordwijk 16-01-1693

Thanks for the document.  I couldn't help but noticed my Antjie Pieters s_gravendijk signed the record with her mark.  It gives a small clue to her ability to read and write.

In your research, have you come across multiple people by the name of Neeltgen Meijnderts?

No. Meijndert was not a very common name around here. Although there lived a Meijnert Claesz in Lisse in the 1st half of the 17th century but as far as I know he didn't have any daughters. 
A Meijndert Arentsz in Noordwijk who married in 1652, no Neeltge either and besides, wrong religion and not in the same social surroundings.

It sounds like it's almost reduced to a process of elimination to figure this family out.