It's impossible for Noomi to fail at doing an English accent. She's not trying to be English.
Then what is she trying to be? Her character is English. As evidenced by the young Elizabeth in the dream.
I can understand her accent not being English as an adult, as it's implied she grew up moving around. The problem is the inconsistency of her accent in the film.
* I'll try to be more clear. What I was trying to bring up was the idea of a mixture of English accents (which in this case of Shaw would include some words with an English accent).
- While her character has British ancestors, as a child she did not live in England.
I checked a couple of wiki articles and from that; she grew up in South Africa.
Shaw was raised from childhood in South Africa by her father, a missionary after her mother died of unknown disease.http://avp.wikia.com/wiki/Elizabeth_Shaw
Does the adult Shaw have what could be called a South African accent (see "District 9")? No.
- Shaw's English accent is a mixture and as I explained I personally have met people in Sweden who had learned English with an English accept (but I'll add that it was blended with a Swedish accent).
- But this leads to the overall idea of the change of English accents due to not only changes in the environment but also due to the vocal flexibility of the speaker.
And in my career and personal life I've known thousands of people who have moved to different parts of the world and whose English accents have developed or changed in different ways.
- What I've seen is that English accent flexibility varies. Some people like my mother for instance who has lived on the West coast of the US since her 20s, has mostly a West coast accent but still has a group of words which are in a New York accent.
My father by contrast, who left with my mother at the same time, had no New York accent once he moved to the West coast.
My wife is from a Puerto Rican background but she has lived with her family in Germany and the southern US. Everyone in her family speaks English with a different accent. But my wife speaks English with no Spanish/southern accent and sounds like someone from the US West coast.
* Now back to your issue;"The problem is the inconsistency of her accent in the film."
I certainly have no intention of changing your mind about this.
And this is not a problem imo and is one of those agree to disagree situations.
From my POV, I've heard inconsistent English accents with thousands of people that I've met who were born / have lived in different parts of the world and then came to the Western US.
And as mentioned, I included my experience with English accents in Sweden which directly relates to Noomi's background.
- So, Shaw has an inconsistent English accent. I reason, that's fine.
For people who have lived in different parts of the world, inconsistent or hybrid English accents are very common.
But again, I'm willing to agree to disagree.