The word blundered as used in the excerpt above is "to make a mistake". See contextual explanation below.
Let us see the sentence again.
"She was one of those pretty and charming girls born, as though fate had blundered over her, into a family of artisans.
This writer expects the reader to co-assume that pretty ladies belong to the upper class of the society.
Hence the "error" or "carelessness" of fate in causing the nameless protagonist of the story to be born to a poor family.
Thus, it is correct to state that the word "blundered" as used here, means to make an error or a mistake.
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