My sister doesn't use her copy of ACNL much, so she lets me time travel back and forth to pick weeds. But she has the WORST batch of villagers imo, and they always end up moving into my town! The upside is some of my favorite villagers that moved away went to her game so I get to visit them, but it's so annoying when I'm trying to get dreamies and people just keep moving in from the next town over
I guess the best thing to do is when you visit is to have 10 villagers, to avoid any move ins. However, if that's not possible there's no way to really avoid getting your sister's villagers since when you visit they essentially hitch a ride to your town as long as there's space and they haven't lived there previously or are out of your 16 villager cycle. If you have the time and patience, I say since she doesn't use the game much just wait until you've got 10 villagers and then visit. Or maybe clear her void by having her visit you when you have 10 villagers.
The only way to stop that is either always make sure you are at 10 villagers when you do anything on another town or just avoid all wifi and turn off street pass until you are at 10 villagers. It's a problem for everybody and I've had it happen the once, since then I just never allow visitors or visit while I have less than 10 villagers
You could always just ask or post a thread on re-tail or train station(Not sure) asking people if they would allow you to visit to clear your void! Some people may ask for things in return but most allow you to do so for free if you just ask!
