Moon

Selene was known as Goddess of the Moon. If Della was really stranded on the Moon, why didn’t Selene use her god powers or something to sense her presence despite possible limits? She could’ve told Dewey or Scrooge about her whereabouts unless Zeus forbids her from helping them because of his grudge on McDuck. This could’ve possibly helped avoid Della from giving away the plans to the Spear of Selene to General Lunaris to complete the pieces for the invasion.

I think F.O.W.L made the cosmic storm with a weather machine to kill Della and spilt off the family.

Why I think this?

Because in "The Last Crash Of The Sunchaser!" The board pulls Scrooge out of the office (or whatever). First you might think that they do that because they don't want to get McDuck Enterprice bankrupt, but when you think deeply about it they don't want to get the McDuck family be together and decided to stop Scrooge finding Della.

(Excuse me for my bad English. I'm a fourteen year old Austrian girl that learned English for 3½ years)