I added a Phoenix obit for Opal's brother, Charles Raider, Jr. In it is listed two surviving sisters, out of state. It doesn't name them. Checking on Ancestry. com, his sister, Mildred E. Mullendore (mispelled Mullendou in his father's obit), died in 1968. Burial at Yeoman Cemetery, Yeoman, Carroll County, Indiana. The other sister, Janie M. Dickman, died in 2002. Burial at Shrine of Remembrace, Colorado Springs, El Paso County, Colorado
Opal Fulks wasn't mentioned in either Mildred's or Janie's obituaries as a survivor. One would conclude, then, that Opal was no longer living at the time of her brother Charles' death on 21 Oct 1966. So we can assume she died before Oct 1966, which would narrow down her time of death. This all the more reinforces the possibility that her immediate family knew she was alive after her alleged disappearance in 1931. Since they knew where she lived and that she was still alive in 1957, we can place her death between Oct 1957 (her father's death) and Oct 1966 (her brother's death), a window of 9 years.