Yes, could be that she is just hard up.
I don't think it's all that unlikely that the Kennedys were behind it, but I don't know how on earth anyone could prove it.
As you say, this combines elements of the story that were already out there, the only new addition being that it is someone in DiMaggio's family who wrote it.
DiMaggio was an honorable guy, who always had my respect. But it could be that someone needs some money now.
To my knowledge, DiMaggio never utter one word about this; she should have followed his lead.