Really? You didn't mean to plagiarize, so that should make it ok?

I have a student. Poor writer. Poor, poor writer. She is likely going to earn her master's degree. I have a problem with someone who writes this poorly 'earning' a college degree. How did she get an undergraduate degree? Anyway, I was reading a draft of one of her papers and found a sentence that was obviously too sophisticated to be her writing. So I googled it and found an exact, word-for-word match.

I sent her a stern email explaining the seriousness of this. I blah-blahed about how plagiarism has nothing to do with intent; it's outcomes based. "If you don't attribute a phrase, sentence, or section of writing to the original author, it's plagiarism." Period. I assured her: "I'm not accusing you of purposely trying to claim this sentence as your own. Perhaps you forgot. Perhaps you didn't think you had to be that careful because it's a draft." Etc.

Now, mind you, this student used direct quotations with QM and citations throughout the paper. Here's an excerpt from her return email: "I didn't mean to plagerize at all. I can't believe it happened I have never been accused of plagerizing." (Her error, by the way, leaving out that period between 'happened' and 'I,' resulting in a run-on sentence; see what I'm dealing with?)

Okaaaaaaay. Did you read my email about intent not having to do with it? Did you read where I said I wasn't accusing you of anything? But as long as you brought up what you didn't mean to do, can you tell me what exactly you were meaning to do when you copied word-for-word that section from a brochure(!)?