God Deals With a Snake and Saves
This girl's declaration wasn't free publicity for Paul and Silas. It would have associated their message with the occult. There is a real spiritual battle taking place. Paul and Silas are flogged and wouldn't have been able to move, let alone escape. Locked up, they sing and pray; the gospel can't be locked out! The jailer asks what he must do to be saved. The gospel changes him immediately.
The video of the entire service including recorded Hebron congregational singing can be viewed here.