Either that, or Bo Peep actually went looking for Woody and friends, and so went back to the house that she knew, of course unaware that Woody, Buzz Lightyear, and the gang, all have a new owner now.
Bo Peep was actually part of a lamp that was in the room of Andy’s sister Molly.
The fact that the toys have apparently reunited there could indicate that Bo Peep never left the house, maybe she had been simply put in storage.