Why do people hate this character?
Because a lot of people are fed up with these brainless, bitchy beauties which the film industry serves us on a golden platter.
Anna is one of the prime examples what makes a character worth hating.
It's not, as some might think, that we dislike strong female leads - because Anna is not a strong female lead.
She can survive crashing into a tree, falling from ridiculous heights and swing over chams. That does not make her strong, it's just a set of action scenes her character is in. She is not a half-goddess, a mutant or some other supernatural being, that would make these abilities plausible. Instead it's only annoying.
There isn't anything in her character that makes her strong. She is not even brave as some say. To be brave would require doing something that a person knows is to be dangerous or would have severe consequences for her.
Anna is not smart enough to grasp the concept of danger, she just a silly girl who acts and speaks without even pausing for a minute to think if it might be useful.
A strong character would not mind help, but she is an insecure, bitchy brat who needs to do everything by herself just like a five-year old who has decided that it has to do the shoe laces by itself and nevermind the fact that it takes hours instead of seconds.
Apart from her "special" powers, her clothing and her attitude are also totally out of place. Nobody who is seriously into hunting werewolves and vampires, would run around in the woods wearing high-heels and a corset. The danger of the heels breaking and the general uncomfortableness to the feet are just two points, but even more important is the fact that with a corset at that time she wouldn't be able to move rapidly at all.
The whole character just stinks, some might like loud mouthed bitches in pretty things with a silly attitude, but other do prefer quality.

