Can't disable printer sharing

So, I don't own the MacBook in question, but my (not that tech-savvy) sister does. She's moving into her college dorm next Monday and will be bringing her own printer, and I'm trying to find a way to prevent people who aren't her from using it. She will not be bringing her own router and will be connecting the printer to her dorm wi-fi, so we're not going to have access to the wi-fi settings or anything like that. We've tried the suggestions in this thread and even after closing Settings and restarting her machine, I can still discover and print to her printer from my Windows machine, so something isn't working.

So, what can I do here to make this work? I don't exactly want her to have to mess with this herself at college. Here's an Imgur album of what the printer's settings are now, and her system specs.