God did come down and tell us He exists.
It was about 2000 years ago, in a town named Bethlehem…
When St. Luke said that “Mary pondered these things in her heart,” it is generally accepted by scholars that he was saying, “And I learned this stuff from the Virgin Mary, and my interpretation of it leans heavily upon her interpretation of it.”
There was a fair amount of literacy among some Jewish women. St. Paul’s teacher Gamaliel famously had a wise daughter who is quoted in the Talmud. Whether or not Mary could actually read and write (possible), she certainly was able to speak about God in a religiously educated way, and she was able to compose inspired poetry. So she was a woman of letters, whether or not she could write.
Of course, in the ancient world, plenty of literate people made a point of not writing anything themselves. That’s what you had a secretary or a hired writer for - to take dictation and maybe smooth out your style. Making good speeches, or being able to make witty replies, was the real proof that you were smart. (Or a little piece of verse for fun – although actually becoming a poet was just asking for people to think you were pretentious, unless you were really good.)
In the ancient Roman world, everybody wrote letters, because there was a good postal system and a fair amount of travel and people moving away from home. We have lots of letters by ancient women, including the wives of Roman legionaries sending birthday party invitations to each other. (There are tons of letters by Christian women in among the works of the Fathers, too. I’ll tell you why later.)
There weren’t many women authors in antiquity, but there were some. Most of them were Christians. There are some odd bods, like the poetess Proba who rewrote Virgil’s Aeneid to become a saga about Jesus. (Rearranging lines from Virgil to say something different – like rearranging puzzle pieces to make a different picture – was a big literary game in later times in Rome. It’s called “cento.”)
What was more common was for a woman to be a Christian philosopher or a Christian teacher of likeminded consecrated virgins or widows, like Macrina or the Desert Mothers. These women’s words were recorded usually by others. There were also a lot of cases of a scholar/student writing letters to noted people of the day, like St. Paula and St. Eustochium writing to their buddy St. Jerome; it’s really a collaborative thing where they push other people (St. Jerome) to write books or essays about topics that interest them. There were also the “advice column” type letters by women, where they ask some famous saint’s advice about their marriage or their kid’s education, and get an answer back. We have a lot of those. There are also some biographies of saintly friends or legends of the local saint, some of which were recorded by women (usually early nuns).
The most entertaining ancient book by a woman was Egeria’s big honking travel letters to the religious sisters back home, while she was out on pilgrimage. Whoever she was, she was very Christian, very touristy, very talkative, pretty darned rich, and very capable of pushing around nice Roman officers in Constantine’s okay-for-Christians Empire. She traveled all around Egypt and the Holy Land, and got full value out of it. I love Egeria!
So yeah, Mary could have written something. If she had, it would probably have been a letter to St. John or one of the other Apostles or disciples, asking him if he was eating well enough and staying warm on his mission trips, bugging him to write his mother back home in Judea or Galilee, and suggesting sermon topics.