They weren't legally married. The first time she was still married to Tom Fisher, and the 2nd time, the lawyer never filed the paperwork. There is certainly legal precedent in real life for children to battle the widow over an inheritance, Anna Nicole Smith comes to mind.
I had the impression that Mamie and Dina were on the cruise together, so either Mamie works for Dina now, or is retired and socializes with her.

