I'm almost 100% sure that a person cannot adopt another town's campsite visitor. I tried to do it before and it didn't work, but correct me if I'm wrong!
Hey, Hun ... Here is a snip from an information site on this:
... Is it possible to invite a camper from someone else?s campsite?
No, you cannot! I see this question / request posted a lot, and it?s just not possible. You will never be able to invite a villager from another town?s campsite, only your own. Sadly, this also means if you see a villager in your own campsite that you want but have no room in your town, you cannot have a friend come grab the villager for you.
Sadly, no matter how sweet and desirable the Villager my be (like Deena) ... It just can't be done ... Hope this helps