The disappearance of a character from the Vault. (Fallout Shelter)

I had 15 people in the Vault, and one day the sixteenth came to me, without hesitation I sent him to the room with the generator, then decided to check how my expedition to the wasteland was. When I returned to the generator, the girl was not there. I started looking for her everywhere, checked every room, every corner, but she was nowhere to be found. The number of inhabitants indicated 16, but when I decided to recount them by hand, I counted exactly 15. Where did she go? How to get it back? My theory: she was laying in the elevator.