That's really not correct. If the question is: Whom do I love? then the answer is I love her/Я её люблю. In fact, whom (which is accusative) is better paired with её and "to whom" is paired with ей.
Your example only works because the two verbs have different grammatical properties. "help" takes an accusative object while "помочь" takes a dative object.
I understand that "ничего" is the genitive, with "ничто" being the accusative (same as nominative). But I would have expected accusative here since знать acts directly on "ничто". So now my understanding of "direct object" has to be revised.
Is it because it is a negative sentence? Does the genitive always pop up like that in the negative or is it only for что/ничто? Does it happen for other verbs apart from знать?
This sentence makes me think that it will probably be like:
Я знаю Марию "I know Maria"
Я не знаю Марии "I do not know Maria" (genitive appears because of the negative? I am copying the example sentence here... I thought accusative was used also in the negative).
And the same for люблю I guess... I need the help of an expert now :P
It seems that ничего is now preferred to ничто even for genitive and accusative uses outside of literary work and idiomatic speech.
This thread on the topic (or what I could manage to understand of it, anyways :-P) is pretty interesting: http://rus.stackexchange.com/questions/37548/Ничто-не-интересует-или-ничего-не-интересует
I saw a comment in another thread which stated that the direct object of negated transitive verbs is usually cast in Genitive case. Here is probably an example of that. (According to Katznere's English-Russian-English dictionary, ничего is the genitive form of an indefinite pronoun), so here we have a pronoun direct object of не знаю, a negated transitive verb.
Negation in Russian, from what I've picked up, is a tricky subject when it gets more complex than нет [genitive thing].
"ничего" is "не́чего" in the dictionary. https://dict.leo.org/russisch-deutsch/%D0%9D%D0%B5%CC%81%D1%87%D0%B5%D0%B3%D0%BE