It seems like she 'takes care' of her phone like the mafia 'takes care' of its competition. Without you observing the phone at every moment for the whole day, there's no way you could say that she's treating her device properly. If she puts it in her pocket like you says she does, that excessive scratching on the home button can be from a metal rivet that jeans (or similar pants) have that rubs against the glass as she's walking around. And seeing as how women's clothes have smaller/shallower/nonfunctioning pockets, and lots of women walk around with their phones in their rear pockets that's definitely a possibility. The swirl marks could be from her putting it into a purse without checking to see what else is in there (loose particles of sand or dirt like the other commenters have suggested), or by her putting it face down on a table without checking to see if it's clean. And those scuffs on the bottom rear and top front seems like awfully convenient points of contact if she were to put her phone into a car's cup holder without checking to see if it's clean first.
An issue with the coating could (in theory) be a possibility but I'm more convinced it's user error. I just hope that the fingerprint sensor still works despite it being all scuffed up like that

Also, just a tip for you and anyone else that wants to post up phones showing scuffs/scratches (or lack thereof): clean your phone and put it in proper lighting! I know our phones are fingerprint magnets but still...