One will send letters tomorrow? That would be excessive, I guess. And I imagine that in America "one" used impersonally or as a gender-neutral pronoun, active or passive, might be seen as pretentious or haughty. It is possibly used more in the UK, but still much less than in former times. It's a pity, though. Why should Germans enjoy the undoubted benefits of man and the French those of on while English speakers dodge around a useful tool? One ends up missing their opportunity, don't you?
She is saying "litreachaí", using a slightly different plural ending. The current speaker does this in a number of exercises where the plural ends with an "a", but she pronounces them as though they end in "aí".
(there are other exercises where she pronounces the same words with the "a" ending)