The Roommate by Jen Silverman

Sharon's never broken a rule in her life. Robyn's broken most of them. When a recently divorced, buttoned-up Iowa homebody takes in a mysterious, fast-talking housemate from the Bronx to help pay the bills, her quiet Midwestern life gets a serious shake-up. Polite small talk quickly gives way to deep secrets — and even bigger surprises. The Roommate is a dark comedy about two very different women who clash, reinvent themselves, and discover that sometimes the biggest risk is opening the door to change.