Matilda McDuck is the middle of three children. She was still a child when her 4 years older brother Scrooge left Scotland for America. She left Scotland and went to America with her sister Hortense in 1920. From 1902 to 1930 she, Hortense and Quackmore worked for Scrooge. Around 1908 while Scrooge was on a trip abroad they hired Miss Emily Quackfaster as Scrooges new secretary.When Scrooge finally returned to Duckburg in 1930 she and the rest of the family prepared for a nice reunion, but because of Scrooges unpleasant behaviour when he returned she left him, together with the rest of the family...
In A Letter from Home or The Old Castles's Other Secret Don Rosa shows that some time after Scottie McTerrier's death in 1948 she took the job as caretaker of the McDuck-estate in Scotland wihout letting her brother Scrooge know about it. Some people have argued that this contradicts the theory of her being married to Ludwig von Drake. That conclusion may be to quick. This story takes place in the mid-1950s while Ludwig doesn't appear in Duckburg until 1961. Thus the two may have been married after the incidents told in A Letter from Home or The Old Castles's Other Secret or maybe they were already married - when Matilda could hide for Scrooge the fact that she was his own employee she could also hide the fact that she was married.
Don Rosa wanted to use Hortense in "A Letter from Home" but Disney banned to use Donald's mother in a present-day story, so Rosa used Matilda instead. That's why Matilda in such story tends to have some temper more similar to her sister's one, while she was the calm sister in Life & Times.
Matilda tends to have a flower eiter on her hair or on a hat. These flowers are constantly losing petals. While Matilda doesn't have any flower on her hair in "A Letter from Home", she is briefly seen cultivating similar flowers.
As a tribute to Rosa, Marco Gervasio, creator of a series of Duck comics featurting the gentleman-burglar Phantomius, taking place in Duckburg, 1920s, gave Matilda a cameo appearance in one of his stories. She could be seen sitting in the audience of the D.U.C.K. theatre (yet another reference to Rosa), together with her sister Hortense and her brother-in-law Quackmore.