"She doesn't hear this" is very awkward.
Changed the default to 'cannot hear'.
Where it the difference between "tego" and "to"?
Cases, as usual ;) "tego" is Genitive (Nie słyszę tego), "to" is Nominative (To jest smaczne) or Accusative (Słyszę to).
tego = it = this....are both acceptable. Why?
Yes, they are, 'cause they mean the same.
Why is "she doesn't hear this" not accepted, but "she does not hear this" is?