"I do not love this woman."
Translation:Nie kocham tej kobiety.
If I remember right, ta is nominative form and we for some reason need genitive form here. Apparently what you love is not (ackusative) object as I think is in germanic languages but something you own in polish language. Hmmm... Ah wait it is the negation that makes it genitive instead of ackusative.
For most feminine nouns, Genitive singular will be identical to Nominative plural.
As for 'different endings for different meanings'... Well, we just know what the given ending is, we do not think that "oh, this one will be identical to that one". To us, they are 'different endings that just happen to be identical' ;) But for a learner, I believe that's actually helpful to have some rules showing which ones are identical.