Why would historians want to analyze the diary of a plantation wife during the reconstruction era

The plantation wife was experiencing the direct change in social, economic and cultural factors that happened during the reconstruction.
 (such as new regulations that are required for them, type of business dealings that her husband made, how things changes between the ex-slaves and ex-owners, etc)
Because of  this, the diary that  the wife has writen could be considered as a primary source document that depict the reconstruction period.

The Utrecht Psalter