I need to know if I understand this.
The female human - Audrey - exists in the Barn. The Barn stores the energy of the Troubles. After 27 years, the Barn is depleted, and the Troubles begin again. She is sent out to gather the energy of the Troubles and transfer them back to the Barn. I think I missed something.
Actually, I think it's more like this:
The woman is immune to the Troubles. The Barn acts an amplifier that projects her immunity to the entire town, but after 27 years she runs out of anti-Trouble energy and has to leave the Barn to recharge herself with, er, Love . . . .