Possessed Girl In Dream?

Last night I had a nightmare I guess you can say and in the nightmare I had a younger step sister. Minutes into it I started realizing things about her. She kept wanting to play with me then after a little i can to realization that a demon was inside her. When i found out, it knew that i knew and it just smiled at me. ii smiled back, because i didnt want to show fear. I continued playing with her but seconds later my dad came into to the room asking to talk to me, so we went outside and talked and i cud feel her listening to our conversation to see if i was going to say anything, but i didnt. I went back into her room and we continued playing and she took out a knife from under her bed, then a butter knife but once again i didnt wanna show fear so i went along with it and said "u cant do anything with a butter knife, you shud just keep the bigger knife under your bed, its way better". she jst laughed then my dad came in telling us we had to go to bed now. and we said ok. she then showed me her back and it was filled with tattoos of symbols i cant remember and i ran to my dad to tell on her, but then i stopped and told him nvm because i knew it was just the demon and those tattoos can disappear rapidly. i went back and told her i wont tell, but i was going to go sleep so i was going to go to my room and i said "i love you" right then and there her eyes turned pitch black. i said it again and with a smirk this time because i knew it made the demon angry. i said "what happened you cant say it? hahaha" her eyes continued to be pitch black but i ignored it and went to turn off the light when the light switch was already turned off and she just looked at me and smiled because she was the one keeping the light on. i laughed and went to my room thinking everything was okay because i showed no fear but in reality i was scared. i laid down and look away then back and she was there. she knew i was scared because i wasnt able to sleep and thts all she wanted to know so she jst walked back to her room. and yeah i woke up. what can this possibly mean?