Runner enters dugout

Question
Theres a runner on 3rd base and the batter hits a foul ball but the umpire doesnt call foul ball, so the runner at 3rd thinks it a pass ball she scores and goes in the dung out. Then the umpire says it a foul ball. He puts the runner back on 3rd base. The other team says she should be out because she went into dead ball area. I would think the runner can go back because its a dead ball. Is that the correct call?

Response
The runner should be placed back on third base.
If a runner abandons their base and enters the dugout, then they are out. (8.18.Y)
However based on your description, that rule does not apply.