Lin Qiao knew that Si Kongchen was able to sense any living being at a lower level than himself. She wouldn't be able to hide from his radar if she were an ordinary level-eight zombie or human. However, she also remembered how she approached the level-nine monster in the underground world using her invisibility without being spotted. Based on that, she figured that Si Kongchen shouldn't be able to detect her presence either.
She still stayed alert, though. She wasn't sure if Si Kongchen would be unable to detect her presence like the level-nine monster or not, but she was eighty percent confident about it.
She hadn't exited her space before, because first, she wanted Si Kongchen to think that she couldn't escape under his watch, and second, she was waiting for things to change on the outside.