Translation:You are reading the little girls' letters.
Of course! Even in French, the same preposition (de) is sometimes for possession (like Engl. "of") and sometimes for origin ("from"), as in, "Elle est de Paris" or "Elle vient de Paris," both of which are translated as FROM Paris.
In English, "letters FROM a person" is a perfectly idiomatic expression.
This is part of what my French penpal wrote in one of her emails. She doesn't speak any English at all, so I have to write to her in French and she's always written to me in French. Years ago she wrote a few letters to me in English and I couldn't understand her English at all. I could understand her better in French.
I thought she meant "grand-daughter." She doesn't have a hyphen in between "petite" and "fille" but it still means "grand-daughter" in the sentence. Virginie is one of her daughters.
One of the reasons why I'm doing French on Duolingo, is to keep my French up, so I could write to her. I have no problems understanding her letters. I just can't write what I want. I tried Google Translate sometimes, but it makes lots of mistakes.
"j'ai une petite fille de plus, Virginie a eu une fille le 5 Octobre elle s'appelle Manon, je vous enverrai des photos"