Can I be in my room alone with my cousin female me male?

Salam, we are both muslim, I am a guy and she is a girl, they come twice a year to our house, she is my cousin. I was wondering if it is permissible to have her in my room just me and her with the door open we just want to talk and play things and there are people around the house. I know of the sunnah that shaatan will be a 3rd but since we are having the door open and people are still around the house is this okay?