Sorry, what makes it shallow of me to ask ?

I'll be honest, given the number of books in a library (let alone several libraries) I expect there are things in there she has not read. She could also consider re-reading books. Maybe you could put into perspective, just how many books is she reading in a day ?

Beyond that, it might be time to start paying. Buying singular books can be expensive for someone as voracious as your wife, so maybe something like Kindle unlimited is the way to go - thousands of books with new ones popping up all the time.