Did you report it? I just did.
Your sentence is perfectly perfect and common English grammar as emery noted.
If you deny the verb, then it’s perfectly acceptable to use "either ... or" for emphasis.
So, it's Duo being short-sighted or stubborn for not having accepted it after a year...
Triple negative: Don't ... neither ... nor ...
is seldom because it's wrong English grammar.
Either one denies the verb OR the conjunctions, but not both.
Eat neither ... nor ...
Don’t eat either ... or ...
I guess Duo is trying to make us use 'neither . . . . nor' but this is being excessiveley literal it is transliteration, not admitting other correct (and more common) forms in English. 'She eats neither . . nor . . ' doesn't sound to me like the way American speak, but maybe one will correct me?
According to Modern Brazilian Portuguese Grammar (John Whitlam, Routledge, 2011), "either...or" can also be used for "nem.....nem". Here's an example that's included in the book (page 106):
"Não tenho aula nem hoje nem amanhã." I don't have class either today or tomorrow.
The reason seems clear: "I have class neither today nor tomorrow" is not what most native speakers would say. It's not wrong, it just sounds needlessly formal and a bit archaic.
The same is true of a sentence like "I have neither my checkbook nor my credit card". It's correct, it's just not what we would usually say.
So based on this, I suggest that "She does not eat either chicken or fish" should be accepted.
What is the reason for the radical change between the phrase, for example, "The girl does not drink neither juice nor milk" and that phrase that I repeated, practically the verbiage "She does not eat neither chicken nor fish" and was not accepted ? Can they position me? Is it just a different way of forming the phrase? I think my answer should be accepted or at least have a reasonable explanation for it not to be.
Now I'm doubting myself and my English grammar knowledge! Can't either and neither be interchangable? (Like flammable and inflammable both means that whatever it is, it will catch on fire.) If either and neither are NOT interchangeable then how to know which one to use? Also, I started this sentence with " She doesnt want...", but that seems to be wrong too. Can anyone help me?