Why she is mean?
That question is easy..... She wants to be the star of the whole thing. Like I said up there she is a drama queen and she wants to be popular and people who want to be popular are kinda mean (well that's what I saw).
In the show.
In Boast Busters she is a bragger and in Magic Deul she comes back to challenge Twilight and takes the Alicorn Amulet and cheats in the challenge and makes Twilight leave PonyVille but luckiley Zocora teaches Twilight to use magic but well she cheats too but it was Trixie's fault like a little kid... SHE STARTED IT! Anyways she kinda reforms at the end of Magic Deul but I guess sents she never did that in the human world she never acts nice in EG2. Anyways have a great day and let me know what you think of Trixie bye!