This Corrosion (2003)

It is the Winter Solstice, and Farrah Klement was released from the sanitarium three days ago for her birthday. She marks the occasion by going off her meds and driving upstate to celebrate her birthday the same way she has every year since high school-- with a full Solstice moon overhead and a pagan bonfire with her circle of aging small-town friends. But this birthday is different. Farrah has arrived at the party with a mysterious woman in a wheelchair, with no knowledge of who this mute woman is or where she came from. While we lurch backwards and forwards in time across Farrah's mental trajectory, her ne'er do well friends carry on with the night's debauchery, and Farrah begins to tie together the disparate pieces of the metaphysical puzzle-- a ringing cell phone, a violent fight with her sister, an approaching police car-- only to unravel an even darker riddle.