I think she is mentally the strongest vampire, we've ever seen. While Elena (the whiney do-nothing) had all of her friends to comfort her when she was feeling down, katherine had enormous trust issues, because she couldn't trust anyone. Like it's so unfair, what's her fault? Not wanting to die? She couldn't even holde her baby once, not even once, because she had it out of wedlock. I myself can speak bulgarian and the way she said it, the words that were pronounced, it was heartbreaking. Then she fled to england and klaus wanted every drop of her blood just so he can ruin the damn curse his mother had put on him. And you know what the curse was? Removing his werewolf side. That's right, he wanted to kill katherine, just so he can also be wolf again, the thing that bothers me is that we never really got to see him turn. Katherine ran like hell, she had only one thought in her mind ,,survive''. And unlike elena who fell inlove with damon, katherine's love for stefan had always been real. She cared for him, deeply. I like katherine so freaking much, because she has suffered the most. She will forever be my favourite character, rest in peace wherever you are!!!!