In Elly's time, the ability to read and write was more-so only accomplished by those of wealth and position.
Despite suffering from mental illness, Elly possessed higher than average intelligence. In example, the ability to read and write, usually only practiced by those of privilege and wealth, Elly had the good fortune to learn English, to read and to write in her time at St. John's Chapel, having been taught by Father Tierney. She also had studied the masters and classics of literature, having nearly memorizing all that she read.
Had IQ testing existed in her time, Elly would likely have displayed advanced intellect and aptitude.
Interesting, and ironically to note, Veronica Franco (1546-1591) was among one of Elly's favourites. Franco wasn’t simply and ordinary courtesan, but was educated and a talented poet as well. She defended herself successfully against charges of witchcraft. She was married to a doctor briefly and later became a sex worker to sustain herself and her children.
There is a reason for this post, in that it reflects what is coming next in the extraordinary layers Elly Kedward possesses.
Of the several years Elly spent either incarcerated or committed, there was no doubt ample time for... well, basically nothing.
What that displayed was massive room for one hell of an imagination.
...and we're going to discover that thoughout Season Seven, coming next...