Shakespeare's Trollop by Charlaine Harris

Cleaning woman and karate expert Lily Bard is a woman with a complicated past. Trying her best to cope with her terrifying memories and horrible nightmares, she decides to join a weekly group therapy session in her hometown of Shakespeare, Arkansas.
At first, Lily can hardly believe the number of her fellow Shakespeareans who share her life experiences. As it turns out, the group members' feelings aren't the only things that need sorting out - they assemble for a session and find a woman dead, killed in bone-chilling fashion and deliberately left on display to send a twisted message. Who would commit such a horrendous crime, and who is the intended recipient of the message?