If you have not found any answers yet, perhaps this will help.At www.ancestry.com I found:
Lansing, Isabel Katherine, female, b. 22 Aug 1906 in Nebraska, female, mmn Heisner, father: Bader, ss#552-68-4395, d. Orange County, CA 26 Nov 1995.
Have you tried obtaining her death cert from Orange County?It would list the person reporting her death, which would probably be a family member.You can learn the cost and where to write by going to www.vitalrec.com.
Also, the Orange County Register newspaper would prob have an obit for her.
I don't know if you have worked these angles, so am suggesting them to you.