Should I make my aunt sign a lease? (Roommate)

With the duplex I just bought, I'm going to be moving into one side. My aunt was going to move in with me. She will be paying me 400 a month. I was just thinking about writing up a lease agreement between us just to be safe. I trust her and don't think she would try anything but I just want to be SAFE. What do you guys think? Also, if you think I should write one up, under what terms should they be in? I want it to be a simple but a clear and understanding one.