Hi @tac0s
The ones I’m referring to are linked in the guide on how to approach a professional.
First of all, that should be the headline of the document 
, second, that’s a good point. I’m just assuming if someone who is doing piercings on a regular basis, might be more aware of the typical piercing locations and that this is the reason for the detailed guide with the images and all. But I think you’re more qualified to comment on that than I am of course.
The reason is actually similar to the one you mentioned in why the arm is not an ideal location. Mostly she is concerned about it being in her way when she does something with her hands, like putting gloves on, working, etc.
Her preferred place would be the underside of the forearm if that is even possible to do. It would at least not matter as much for purse straps or backpacks and makes it easy enough to scan with a phone.
Using it for authentication, opening doors, etc. would be a bit awkward, but that’s not that big of a deal for her.