Have checked. To my knowledge, the OP contains every currently published story belonging to any of our local authors (there's been a couple posted here in spoilers, but they were all of the "hey guys, could you go over my rough draft?" variety).
I also feel I should really nominate Bubbles as a Noteworthy Fic. Because it is.
No, Peppermint is what makes her special. If it was the lisp, her Cutie Mark would be a picture of herself spitting on Applebloom.
Really though, it's not like I hate Twist. It's just that I'm pretty sure everypony would read her dialog in her voice anyway, and 's' is such a common syllable that switching every instance of it to a 'th' sound makes reading unnecessarily difficult. Whoever came up with the idea of transcribing accents should be banished, then thrown in a dungeon in the place they're banished to.