"He did not even look at her."
Translation:Nawet na nią nie spojrzał.
I think this sentence is a great example of how word order matters and how hard it is to explain without a particular example ;)
Your interpretation could possibly work if you gave the same (voice) emphasis on "NA NIĄ". Without it, having it as a written sentence with no context, I'd say it's "he totally ignored her, he didn't even bother to look at her for just a second".
I'd translate your sentence as "[On/] nie spojrzał nawet na nią."
"nię" is definitely a mistake, it should be "nią".
"patrzał" is a correct form, but relatively rare - many Polish people would think it's wrong, actually. "patrzył" is the common one.
The word order... well, the usual, we try not to put pronouns at the end of the sentence. It's acceptable, I guess.
The choice of "patrzył/patrzał" makes it more like "wasn't even looking".
If your answer had "nią", it would be accepted with a typo... I wonder if "patrzał" should actually be accepted itself.
It's still accusative, but a post-prepositional form (mandatory after prepositions). It just happens to look like instrumental.