<em>The poor, plague-ridden, residential areas of the town were shut off from the rest of the world.</em>
The words <em>poor, plague-ridden and residential</em> are <em>adjectives</em>, and it is correct to separate them with commas. <em>-ridden</em> (means full of something unpleasant or bad) is a <em>suffix</em> used to form adjectives; in this case, with the <em>noun plague</em> it forms the adjective <em>plague-ridden</em>. <em>Shut off</em> is phrasal verb and doesn't need hyphen.
Aphrodite cast a spell on her. This is shown when Helen later speaks on the matter saying she regrets leaving with Paris and her husband Menelaus says he forgives her because Aphrodite can do that to people.
