The environment in which a person grows up affects them for life. Soran may not have much memory of her father's death, but her mother's attitude during her upbringing, and the fact that most of her playmates experienced the same pain, surely impacted her psyche.
Although Zone 019 did everything it could to handle the aftermath of the mining accidents, and over time, it seemed as though these pains had been smoothed over, the people of Zone 019 generally have longevity, and there must be things that neither consolation nor time can heal.
During Soran's upbringing, the frequency of mining accidents rapidly decreased, and when machines replaced most of the people, there were almost no more accidents due to mining. An ordinary person might have buried these negative things deeper in their memory over time, but Soran was exceptionally precocious, and her excessive emphasis on positive emotions instead seemed somewhat incongruous.
