Well I'm no expert on English dialects/accents, but needless to say I think she's a terrific actress. Very classy, sweet and funny lady indeed, so I could care less if her accent is spot on or not in the film. I think many people/movie critics obsessed on her accent instead of the actual story itself which seems to be beautiful. Just my opinion 
I do like Anne Hathaway, but the problem with an inaccurate accent is that it distracts from the actual story/dialogue and then you can't concentrate on the plot... you start wondering how a character born and raised in Northern England can have an accent that is half-American and half-Southern English... and then you start listening for how badly each word is pronounced and wondering why the native speakers didn't point it out during filming

. It might not be an issue if you don't know how the accent is supposed to sound, but when you do, it's hard to take it seriously and believe that it's a 'real' story with 'real' characters.
It was the same sort of thing when there was an American character on Spooks last year but she was played by an Irish actress... I think the character was supposed to be from Boston, but the accent seemed to switch between some weird mash-up of several different American accents and an English accent all at the same time!