DG had an awfully high bar to leap, as a character, to match Dorothy as Baum portrayed her.
Forget Judy Garland's Dorothy for a second. In the books, Dorothy was around eight (or, by the canon, eleven ... but she acts more like she is eight) and tough, strong, level headed, and matter of fact.
Dorothy is a child that adults defer to in decision making (and even in life and death situations) because Dorothy is brighter, wiser, and more level headed - or more courageous - than they are. Sometimes, even powerful and wise beings like the Wizard of Oz, Glinda, and Ozma defer to Dorothy's judgement, and sometimes she has rescued these people from their enemies.
Dorothy also takes no lip from adults, who would lord it over her simply because she is a child or because they think they know better than she does. She is quick to call people out for what they are, if they behave foolishly, stupidly, or inappropriately, and accepts the consequences stoically.
Read the books. They're good reading. And all of them are available for free (because the copyright in the United States has expired) at Project Gutenburg (you can link to it from Wikipedia ... type in The Land of Oz, Ozma of Oz, or another book name for the Wikipedia entry.)
(remember our 3rd IR?)
