Hello Anneke,
I hope you can read English with no problem. I have some information for you and I hope it is helpful.
1940 Census, Los Angele, California
(adres) 2032 South Highland Avenue
-Coons, Cecil F.; age 35, born in Iowa, occupation of Electrician, renting house for $25.00 per month
-Coons, Anna; age 25, wife, born in Holland, occupation of Cashier in Department Store
-Coons, Beverly June; age 5 years, born in California
-Boardman, Betty; age 50, mother-in-law, born in Holland, no occupation
Living next door to the Coons family:
-Boardman, Jack; age 27, born in Holland, occupation of Mechanic
-Boardman, Dorothy; age 23, wife, born in Illinois, no occupation
-Boardman, Betty Ann; age 3 years, daughter
So, it looks like Pietertje Baardman- Kooij (Betty Boardman) is living with her daughter, son-in-law, and grand-daughter and living next door to them is a son of Pietertje Baardman-Kooij with his wife and daughter. Both grand-daughters are name Betty which I am sure is after their grandmother, Pietertje (Betty).
This is Anna Maria Coons-Baardman death information:
Died: 9 November 2001
At the time of her death she was living in Chatsworth, Los Angeles County, California
Anna became an American citizen on 13 November 1942 in Los Angeles County and was living in Burbank, California at the time.
Anna's brother Jack Boardman (I think Jacob Baardman?) was born 9 January 1913 and became an American citizen on 4 December 1942 in Los Angeles, California. He was living in Los Angeles at that time.
He died 1 January 2007 in Culver City, California.
Maybe this will help a little bit with your search!
gr,
John