Marie claims she can predict the sex of pregnant women's babies

Marie claims she can predict the sex of pregnant women's babies. She sees 1,000 women a year, and she always predicts a female. She charges $1,000 for a prediction, and she always predicts a female (although clients do not know that). When she is wrong, she offers a double-your-money back guarantee. Since the chance of having a female is approximately 50%, how can she earn any money?