Italian uses the definite article in quite a lot of places where English doesn't. There are a lot of times when two English sentences would translate to the same thing ie. "Fruit is sweet" and "The fruit is sweet" are both translated with "La frutta è dolce"
I don't fully understand why but "almeno cena è pronta" just sounds wrong. Possibly it's just one of those odd differences between languages that you have to get used to or possibly someone who is more fluent in Italian would be able to explain why.