The Legend of Annie Murphy (Cooper Kids #7) by Frank Peretti

In 1885, the Murphy mine struck gold. According to legend, Annie Murphy killed her husband out of greed, but just before she was to be hanged for the murder, she escaped. Now, a hundred years later, there have been sightings of Annie Murphy's "ghost." The Coopers unwittingly become involved in a mystery that finds them caught between the past and the present.