Translation:She never appeared here during the day.
It's not that easy. Generally, it could be on either side of the verb, but it cannot start the sentence and it shouldn't end the sentence. But sometimes one of the versions sounds a lot better than the other one and there isn't any real reason other than 'it just sounds better stylistically'.
But it can also be divided from its verb by several words, even. Just like here. "się tu nie pojawiła" sounds perfectly natural to me. "nie pojawiła się tu" on its own as well, but then "tu" would land at the end of the sentence and that's inadvisable. "tu się nie pojawiła" is perfectly fine as well.
"się nie tu pojawiła" or "pojawiła się nie tu" would mean "appeared not here", so they're wrong.
Yes. Totally tragic :-). Sorry, immerweiter :-( Prepositions are always a problem. Bizarrely, a phrase like "at six o'clock" would be perfectly fine. I think it's because "daytime" is a period of time, rather than an actual time. So, "At daybreak" works (although it's not what the Polish means, so shouldn't be considered to be acceptable here) as good English, because it is a point in time, rather than a period.
Can you clarify the case, please, for 'za dnia'? Wiktionary shows 'DNIA' only for genitive, but the hint shows it for accusative and genitive. I've looked at various sources on the Internet and can't find the actual meaning of 'ZA' as 'During'. Can you please clarify for me. Thanks.
The hints are incomplete in terms of cases - in fact Duolingo doesn't want us to put cases in hints because it messes with some exercises. Hopefully one day they will find a way to display them in a way that isn't problematic at all, as it would be really helpful for the learners.
"za" here takes Genitive indeed. But it isn't used much in such a meaning, only in some fixed phrases. "za dnia" = "during the day", "za moich czasów" = "in my times/in my days", "za Margaret Thatcher" = "during the time when Thatcher was in power", and a few other usages.