I finished 8th grade, started 9th but left and took the road of the sunburned thumb for a number of years and never went back to formal schooling. Were it not for spell check that would be obvious. So perhaps I'm qualified to suggest a few things.
Theology seems to be tied to philosophy in some of the books I've read, and has required me to look up definitions of word after word. This can be discouraging or encouraging depending on the individual's outlook. Epistemology ..... Antinomianism ....... Arminianism ..... metaphysics ..... ontology ....... a priori ........ aposteri ....... empirical ............ teleology ....... analogous ........ noumenon ........ ad hominem ....... are a few of the words I've had to look up of while perusing books of theology. I found that keeping a piece of note paper handy and writing the definitions down helps in learning them. A smart phone and google simplify searching them out, but a dictionary would suffice if it was a comprehensive one.
So you're never too old to learn if you have the desire. There is an edition of the KJV called "
The Defined King James Bible", put together by KJVO advocate DA Waite, and it is available on his website. The medium size edition is a nice size for toting around and the print is of a comfortable size. Archaic words, within the text, are in bold and are defined at the bottom of the page.
If someone is having a really tough time with reading I might give them the New Living Translation. I have looked through it and it is ideal for those who struggle with vocabulary in my opinion. The NIV is also 'easy' to read and understand, for me anyhow. A study Bible in either of those translations might be a good avenue to introduce a person struggling with reading. In the 1980s I would read the KJV first, then go to the NIV to make sense, in plain English, of whatever was 'above my head.'
For theology, I'm not sure what the reading level might be defined as, but Reverend D. Martyn Lloyd-Jones sermons on theology have been published in 3 volumes, it is now available in a 1 volume paperback,
Great Doctrines of the Bible, . These published sermons are also accessible online so you can listen to them and decide whether they will be understandable for your Mrs.
Great Biblical Doctrines | Collection | MLJ Trust
In my experience it is sort of a pay me now or pay me later situation. Had I applied myself and continued in school 50 years ago I wouldn't need the dictionary. So I'm playing catch up, but that is a good thing. I wish your wife the best of luck with the reading and hope that any suggestions I have made are fruitful.