Celestia sends an extremely smart filly prodigy to Ponyville to spend time with Twilight, Celestia's number one student, in hopes that the two will learn from each other and become friends in the process, but, Twilight doesn't like the fact that some young filly can waltz into her home and overthrow her crown in intelligence.
That ending sentence was not structured well.
I don't know, Twilight doesn't strike me as the type to get jealous.
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I suppose, but then again this story won't be logical at points so...