The question remains unanswered for many Disney fans: were Mickey and Minnie
ever married? John Grant, in "The Encyclopedia of Disney Animated Characters"
states that there was a tradition among the imagineers that they were. Dave
Smith of The Disney Archives says there never was such an understanding.
Most of the shorts tend to imply more of a courtship relationship between
them, but a long standing and steady courtship, with only a few rivals.
(The most interesting from a trivia point of view being Mortimer Mouse from
"Mickey's Rival"; interesting because Mortimer was one of the first names
suggested for Mickey.)
Regardless, Minnie's personality never really got developed fully apart from Mickey. There were only a handful of shorts where Minnie got a starring role sans Mickey (such as "Bath Day", "First Aiders" and "Pluto's Sweater.") Even then, though, she seemed to be in the same position as Mickey; relegated to a "straight-man" role while the other characters got the laughs. In almost all of the other shorts, she was solely defined in terms of being Mickey's girlfriend. Or at least the object of his affections; a role that she seems completely happy with and perfectly suited for.
From Lee Suggs : Minnie was strictly Mickey's girlfriend until at least the 1940's. During that decade Minnie was in cartoons with Pluto, and Figaro. (Yes, Figaro from Pinocchio, somehow he became Minnie's cat.) Two of the cartoons- "Out of the Flying Pan into the Firing Line"(1942) and "First Aiders"(1944)- deal directly with the life of civilian women during World War Two. The first short was a commercial paid for by the Federal Government. Minnie is shown about to give Pluto bacon grease when he hears an announcement that the government is collecting fat for its glycerin. (Which could be used to make explosives.) Pluto refuses the grease and instead has Minnie package it so he can take it to a meat shop for collection. "First Aiders" has Figaro laughing at Pluto as Minnie practices bandages on him so she can qualify as a First Aider. (This was a real effort by the Red Cross to train women to take care of victims of bombing or other kinds of warfare. Of course, they never used their skills since after Pearl Harbor and the Japanese Forces taking of the Philippines and other Pacific Territories, the United States was not attacked during World War Two.) This short is probably the source of "Nurse Minnie" collectables; since First Aiders dressed like nurses. In 1946 Minnie was in one more short with Figaro, "Bath Day". This is just a standard short with Figaro resisting Minnie's efforts to bathe him. While Mickey was not in any of these shorts Minnie was not really the main character. Figaro and Pluto have almost all the scenes with just short appearances by Minnie. In "MouseWorks" first season Minnie finally gets to be a real main character. "Purple Pluto" allows her to make a ridiculous mistake, and then try to literally cover it up. Mickey is in the short, but Minnie causes the conflict and deals with herself. "Daisy visits Minnie" has Minnie dealing with a very obnoxious Daisy Duck, who eventually lets an escaped lion into Minnie's house. Minnie fights the lion and forgives Daisy after it's all over. In shorts which feature both Mickey and Minnie ("Hansel and Gretel" e.g.) Minnie saves Mickey as much as she saves him. So "MouseWorks" has made Minnie a more "modern woman" and much more Mickey's equal. Now if they'd just get the girl a soccer ball.