Actually, no. If you go back and read the first page, there is *no mention* of the woman having kept the picture for a couple of decades. That's an assumption you made. The OP expressly said they do not know whether she knew of its existence/had it for a long time, or had only just found it in 2015 while rummaging through her ex's belongings.
The woman *is* allegedly a victim of this man, due to the domestic abuse she claims she suffered at his hands. She clearly fears others have suffered even worse and decided not to remain silent about it any longer.
As a survivor of domestic abuse myself, I find her story, her actions and reluctance to go to the local police due to their shared past history and his possible family influence extremely plausible.
As for the old adage: hell hath no fury like a woman scorned, statistics regarding violent crimes and the cases in this very forum says otherwise.