My kids always had a key to the house. You had a deal with your daughter. Unless her grades have fallen off, I'm not sure why you would change that deal. It's a power play to get her to act the way you want her to, it will result in her fighting for her independence in which case she will most likely stop attending college. You need to explain to her why the coming home late is a problem. Personally I would be worried for her safety. Your goal is to get her through college and then launch her into the world with an education. Focus on the goal. Be honest with her. You are still her parents but, she is an adult not a child. Treat her like an adult.