you need to move out 16 villagers so whichever villagers you don't want just tell them to leave and then it'll count towards 16 so if you move out 1 you'll have to move out 15 more until you can let her into your town. i would also pay attention to your main street so you know when you've finished the 16 villager cycle
You can either use campers or adopt villagers from the Villager Trading Plaza. I should mention though, a lot of people have trouble getting out their 10th villager. Some say you can never move out your last villager, others say it's possible but just takes longer, and then there's people who say they're just as easy to get out as others.
The general consensus seems to be that it is possible.. But it'll be tricky to cycle 16 with only one villager you can move out. Best of luck if you go through with it!