Recall the Time of No Return[Eng] - page 131

Same here, unless the fighting the changelings that became her friends sent her off the deep end. 
Although if you want to see what Stalin is capable of if he live longer read this: LINK

but people can change when something bad tragic happen

She lived for over 900 years and during that time she was already showing change in her demeanor after her friends died of old age. Something that probably shouldn't have happened since the prophecy said she wouldn't outlive her friends.

The biggest change however didn't happen until 7 years ago, right after a war with Crimson Changelings. She started a witch hunt for Changelings possibly still lurking in the kingdom and supposedly killed over 2000 citizens in the process (I use term "supposedly" because if Twilight is indeed a Changeling, then her killing ponies is a waste of good food. And nopony would go looking for dead ponies.)

The biggest question is how everypony is still loyal to Twilight after such a purge? And how not even the rebels suspects that Twilight might be replaced when this whole mess happened right after a Changeling invasion? And if that is indeed the case, what significance does the propechy serve and how does it tie in with anything when we're clearly dealing with a fake Twilight and not a real Twilight who lost her way?

And if she is indeed a fake Twilight, why would killing the Element Bearers ultimately kill her when keeping them alive is a much bigger risk? For that matter, are the Elements of this timeline truly dead? Because if they died, then she too would've been dead ages ago.