last months rent

[Bella3036]

Our tenant rent is due on the first of the month. After paying the rent she said it would be her last month and planned on moving out at the end of the next month. Then she said it would be the middle of the month she would move. The last month has been prepaid. Now she is demanding 1/2 months rent back and we are not even into the moveout month. What does the law require. There was no written noti e of move out date.