OK, this is a real stretch but I'll throw this theory out there.
Terry's mother is either an atheist or she lost her faith over the years. Christians (eg. Mormons, Catholics etc.) believe in life after death. Perhaps her late mother sensed that death is finality, nothing to follow. Terry's anticipation of learning her mother's hidden thoughts turned into disappointment, bewilderment when the journals were empty. Faith has been shattered!
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