FIRST REVISION: INFECTIOUS, an urban fantasy short story projected to be 3,000 words. First three lines revised below.
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Five-year-old Jong Eun-Yul had been tinkering with the spell all week. She smiled sweetly at the foreign teacher when he handed out the English worksheet, and immediately flipped it over to the blank side. Mouthing magic words so that she could get them just right, she drew the jungle snake that she would let loose in the class.
I don't think you need the first sentence. Maybe just put the name and age into that second one, beginning there. I would like the third to give me more ummm, her. More immediacy, if that makes sense. Something like, The color was wrong, of course, but that shouldn't matter--something that gives the reader a direct thought of hers, preferably one offering foreshadowing, as opposed to to backstory (had been tinkering all week).