Oooh I’m gonna jump in on this one because it’s a subject very close to my heart.
I’m going to avoid this issue of which books to use.
I quit piano when I was a kid because my teacher was a miserable bastard. He had no patience, he had no inclination to make the learning process fun- in short, an evil PoS (I’m not talking Point of Sale either).
The only differences here would be you are the teacher and your student is an adult.If you can be patient, make light of mistakes made, don’t be afraid to crack a joke and laugh stuff off without being insensitive about it, and make it fun and yet still be teaching someone how to play the piano, then I highly doubt in all honesty that it will matter a jot what book, by whichever author, you choose to use.
Learning music when one has no prior knowledge or working understanding of music can look pretty daunting to a newcomer so just take it easy and go with the flow.
I would recommend going to a music store and checking out whatever they’ve got for beginners. I did have some books in the past, and I could have referred to those, but I found those pretty easy to work with. See if you can’t find at least one book that might have a handy cutout or something that indicates what notes are which on the keyboard, and the rest of it is going to be up to you. There must be plenty of ‘em out there!