Knocking on our door

While I was watching TV in the living room I heard knocking on our front door. I was a little scared but I thought it was one of my friends. When I looked out the window I saw it was a woman carrying her purse but I did not know her. I did not open the door I was scared and worried, it was already 9pm so why was this woman knocking on our door when there was no other car in our drive way? Why she was walking in the cold weather maybe she hid her car? You know I heard a story on the news about people knocking on doors to get inside to rob the homeowner so I do not want to take a chance. My husband was not home only me and my children. She knocked a few times then she was gone. When I checked out the window I did not see her anymore. I am not sure if she was one of our neighbors I did not recognize her and the neighbors do not knock on doors at 9pm. whatever I was glad that she left already.