No way! American English and literature has developed brilliantly in its own right.

哈哈！她说得对，英国的英语是唯一真正的英语！

Obviously, some Brits have never come to terms with their decline into irrelevance. *ducks*

Haha, I also heard somewhere that "English language was born in Britain and got sick in America and eventually died in India" , I don't recall the source, but it is what my brother always repeats :D , Anyway I like american english coz it is easier to speak than british!

She's talking about British English versus American English. She's saying that "American English" is just British English, but with mistakes. By "for the avoidance of doubt" she's basically saying, "just to be clear..."