So I've never had Coco as a resident in my town but now she's shown up on my Main Street? Is this a thing?
Voided villagers that you pick up from other towns can show up there, right?
Villagers who move out, voided or not will appear on your Main St.
Have you ever taken a long break from the game? Maybe she moved in and out during a long hiatus.
It's possible you visited another town that had her. I've seen friends' villagers visit my main street at times. It's a nice little treat to sometimes see someone from another town you know pay a visit
I've had that happen before in my town when random villagers will be in Main Street. I always just assumed they'd moved in and out when I took a long break without me realising...it got a bit weirder when it started happening when I had 10 villagers living in my town and no one was moving out but Main Street kept getting random villagers. Glad I'm not the only one...thought my game was being weird.