She's growing.
i dont think she's growing
her body changed slightly in Magical Mystery Tour, now she has a longer neck, legs and horn.
so far she isn't continuously growing, and i don't think they will make her more taller considering how it would further alienate her from the other five
edit: you know, i just thought, when Twilight was telling them they should keep a journal for future readers, perhaps they'll be doing that as the latest new method of end-episode summaries (previously friendship lessons :c). if so, that makes the second season where the third episode changed that aspect of the show, haha