And after Trixie will be totally defeated, she will travel in time to warn her past self to not duel Twilight but past Trixie will not let her speak and she will get the idea that future Trixie tried to convince her to duel Twilight, and so Trixie will loop in time just like Twilight once did, being defeated over and over.
Of course Twilight will win. She's the main character after all. Doesn't mean Trixie won't put up a better fight next time (if there is a next time). None of us know what the MLP writers are cookin up.