Info in the Washington Death Index, 1940-1996:
Name: Martha J Knight
Date of Death: 12 Apr 1953
Place of Death: Yakima
Age: 95
Estimated birth year: abt 1858
Gender: Female
Certificate: 7929

Using this info you can order her death certificate (which should have her maiden name) -- see http://www.doh.wa.gov/EHSPHL/CHS/cert.htm#OrderingThroughCHS