I was not aware that the behavior had been quite this long term.
Typically these types of behavior do start during midlife with the changes and emotional losses that occur; however, as this has been ongoing for many years, the specific reasons can be more difficult to pin down.
Clinically though, there are some patterns that are common to this type of behavior.
The most likely motivation for this is a trauma of some type. Trauma of an emotional (even sexual) nature can be tied to behaviors like this For example: Unresolved feelings of loss, or grief can start a pattern of behavior that helps deal with the emotions experienced during the trauma. It is a way to express feelings without directly dealing with them, much like working out an exercising allows frustrations that are not specific or even conscious to be worked through.
Without a face to face assessment it is very difficult to say what the key past issues were, but I can tell you that with past clients; loss of a pregnancy, sexual assault and even separation and marital infidelity can cause an expression such as you see here.
If this is so, the best approach is to encourage mom to talk with a counselor as this behavior, although innocuous in an d of itself, can be a sign of some other unresolved issues. Steven