I just shoot the visitor when something like this happens. And it's been happening a lot!
But strangely in my case Carla was never involved, it's always the same pale ghoul woman (she reminds me of Bobbi No-Nose, even has a wig), she changes her name and clothes, but she always comes back to sanctuary for another round. It's like Obelix trying to drink the magic potion.
Because of the Bobbi No-Nose thing, at the beginning I thought it was cool, she coming back to con someone else, and get discovered as always, but the disruption she causes almost every day, having the entire settlement trying to kill her protected ass, is getting old really fast.
Now there's a new policy in sanctuary! Everyone is welcome... as long as they kill Bobbi No-Nose!