Millionaira Vanderbucks has only been seen in one place: a DuckTales episode called "Till Nephews do us Part."  In it, she tricked Scrooge into falling in love with her so she could get at his money.  Huey, Dewey, Louie and Webby wised up to her true intentions, however, and tried to scare her away.  During an expedition into the jungle, the nephews played tricks on her to make her think Scrooge's globe-trotting adventures are even more hazardous than they actually are!  The prissy, fastidious Millionaira was horrified and nearly called off the engagement. 

$crooge apologized, and the wedding went ahead as planned.  Almost.  At the altar, Millionaira accidentally told Scrooge (and everyone else!) that she was only marrying him for his money.  Scrooge then refused to marry her. 

As he did so, Goldie burst from the wedding cake with her trusty shotgun and was furious with Scrooge for being unfaithful to their unofficial relationship.  Scrooge was happy to see her, saying, "Goldie!  My true love!"  Goldie was less thrilled to see him, however, and chased him through the streets, shooting at him!

Millionaira was left weeping at the altar, mourning the ruin of her "merger."  Flintheart Glomgold came forward to offer condolences and tell her that Scrooge was a rotten person.  When Millionaira discovered he was the second richest duck around, she decided she wanted to marry him instead!  Millionaira was last seen chasing a terrified Flintheart Glomgold through the streets of Duckburg.

She also answers to the nickname "Millie."