@ijan1
It's a side-story/flashback thingy. This is just my guess after reading it but I think that Theresa is either Miss Leila's little sister that died in the labyrinth and was reborn as a demi-human, or that she is a girl that resembles her little sister that also died in the labyrinth.
Then the story continues on from Ch 2 of the series, where the guy got launched away by Leila.