If you've already loaded up your mayor or any character, it's too late. She will now be stuck there.
There is a way to move the plot around your town, yes. If you know a villager is going to move in the next day or on a specific day or something, you can plot reset to move them around so that if they're somewhere you don't want them, you can try again until you get them in a more desirable spot.
Using today's date as an example, so it's the 21st, you're going to have a villager move in tomorrow, the 22nd, you save and quit on 21st, load your game back up and tell Isabelle you want to change the date/time, or use your 3DS clock if you use that instead, change the date to the 22nd and change the time to 5:59am. When you load up your game, save and quit straight away, then while you're at the title screen, wait about 20 seconds or so, then make a new file. With your new character, run around the town looking for the plot. If you find it and it's somewhere you don't like, just press the Home button, close the game and start it back up and repeat the process. If the plot is somewhere you like, have your new character build a house somewhere until Isabelle automatically saves your game for you, then you can close the game, start it back up, delete the new save and when you load up your mayor, the plot will be saved in the place you wanted it.
...that said though, if you don't TT in your game and play normally day-by-day, you can simply wait until the next day and just remember to make a new file before you load up your mayor to make sure the plot is somewhere you like.
