Ah, Twilight Sparkle. Why do you not hate your friends for what they've done to you? Hell, why has the whole wedding mess never been taken into continuity's account? I mean, in the big scheme of things this was quite a heavy blow and it breaks the whole meaning of "Friendship is Magic", doesn't it? So why? I know, I know. You'll all say forgive and forget, but really? This is what happened as a result:
They were her closest friends and they broke her heart, something that they should not have done without at least getting straight to the source first. And to top it off, it sounds like Celestia meant for this whole ordeal to happen as a means to test Twilight. Why else was there no real apology? Do you remember what happened to Vakama in BIONICLE 3: Web of Shadows when Matau called him out endlessly for getting them into a mess? He joined the dark side. So how is Twilight Sparkle herself not vulnerable to the darkness inside her heart? What's happened to Rainbow Dash in the episode "The Mysterious Mare Do Well", or rather what should have happened to her, has happened to Twilight in "A Canterlot Wedding" and now it's probable that the same thing could happen to Fluttershy in the upcoming episode "Keep Calm and Flutter On".
But yeah, Twilight Sparkle should be elligble to become a major antagonist for all that she's ever suffered from.
"You're not my best friends anymore."
You who I called brother
How could you have come to hate me so?
Is this what you wanted?
Then let my heart be hardened
And never mind how high the cost may grow
This will still be so
Thus saith the Lord