Why was Helen extremely scrupulous about what she wrote?

When Helen was almost twelve, she wrote a short fiction story called "The Frost King."  She enjoyed creative writing and being able to express her thoughts through words.  Unfortunately, Helen was accused of intentional plagiarism with the story.  She found out that her story was quite similar to another that had been read to her previously.  Though it had been a mistake, Helen had to face "a court of investigation composed of the teachers and officers of the Institution" to be questioned about the plagiarized story (The Story of My Life, Chapter XIV).  Helen was young and had not intended to plagiarize, so this experience was devastating to her.  She described how she felt after the incident:

I have never played with words again for the mere pleasure of the game.  Indeed, I have ever since been tortured by the fear that what I write is not my own.

Helen's anxiety about unintentionally plagiarizing led her to question everything she wrote.  Her fears plagued her whenever she wrote, whether it was for school or pleasure.  Helen even worried that she would write someone else's words in letters to her mother.  These fears caused Helen to be "excessively scrupulous about everything [she] wrote" (Chapter XV).