@ATheBuoy42 I have two towns, and while it's been a few years since I got the shop in my second one when I knew what was going on, I feel like I remember specifically experimenting to test whether visiting Katrina's tent in other towns would unlock the shop sooner, but as I recall, it didn't, and it happened according to how many times I visited her tent in my own town with my own player characters, and not visitors visiting her tent in my town, either. Also, I think the mayor has to talk to her again after the twentieth visit, so she can suggest the shop to them, so if you have multiple characters, send in your mayor after you think you might have hit twenty visits, just in case, so you don't have to wait an extra week, or miss it altogether if you weren't sending your mayor to see her at all.
My theory is that the idea is that Katrina is supposed to be gauging whether there are enough locals in the town interested in her services to justify her setting up shop there. So, only visits from locals, in their own town, count toward the shop. That's what I think the reason is behind doing it that way, anyway. ^o^;>