She might still have luck in contacting Kampen directly.
Otherwise, if Jennigje Van Der Snee emigrated somewhere else, you might have some luck finding her parents' names in other records; there are several possible marriages in Kampen on the site so if you knew Jennigje's parents' names or even just her father's name you might be able to get somewhere.
e.g. in case these ring a bell
Lucas van der Snee to Maria Visser, married in Kampen in 1909
Dirk Jan van der Snee to Hendrika van de Heuvels, married in Kampen in 1911
Hendrik van der Snee to Trijntje van Staverden , married in Kampen in 1928
Also if you look there's a 1946 death of a stillborn child to her and Rowland Johnson, mentions Windsor Ontario - I guess he was a soldier in WWII and she a war bride? Both birth and marriage (presuming they married in the Netherlands) would still require direct contact with Kampen but maybe there would be some records in Canada that would be easier for you/her to access.
https://www.kampen.nl/secure/digitalebalie/particulieren/documentenenpapieren/burgerlijkestandafschriftaanvragen/id_35795 - you could try contacting the email address at the bottom here. If your sister in law has Jennigje's death certificate (from Canada, I'm presuming?) that would probably help you a great deal.