Translation:She and I have spoken every day since Friday.
I also heard it like this, but I knew it took an "s" for todos just because of the sentence. A spanish speaker could tell us if, sometimes in speech, the "s" can be silent. I know in my first language we often skip letters in speech...
I think los dias implies that todo would be plural.
Once you are used to the grammar structure, a silent S is no big deal! :)
Todo el dia (all day) vs Todos los dias (every day)
Is the article always necessary before a day of the week? (Also for months?)
That would work, though there can be a different shade of meaning.
Todos los días means literally All the days (every day).
Cada día can mean Every day or Each day.
Cada día es un paso nuevo por la senda de vida.