It looks like many of the theories posited by faithful viewers of Haven are true. Audrey and William share a deep, somewhat dark (if unknown) past and they are responsible for the dawn of the Troubles.
In Haven Season 4 Episode 10 William revealed the reason Audrey always ends up back in Haven.
You gotta get this idea out of your head that you're some saviour here to fix the Troubles. The real you? You made the Troubles. Why do you think you're the one who has to come back to Haven over and over? Why do you think you're the one who has to deal with the Troubles? You made them.