Dreaming about my step sister?!?

i have had MANY dreams of my sister... we are both around 16 and she is very depressed over everyone in high school making fun of her... it makes me cry when i hear all the mean crap people say to her and i usually stand up for her.. but recently we started hanging out ALOT, after cl,school and at home. one night when we were just watching a movie she laid her head on me and i felt it was my job to comfort her, i put my arm around her hoping that she wouldn't mind... she snuggled closer to me and i held tighter :) after the movie she fell asleep and i didn't want to move to ruin the moment so i fell asleep too. after a few hours i woke up to find he laying on my lap. she looked so precious and cute i just couldn't leave :) so i went back to sleep and the next morning she was gone.. but i found her in the Kitchen it was really early and she decided to make us both breakfast, i ate it fast and told her thanks she said no problem and winked at me. i just smiled and asked if you sleeped well, she nodded and we both smiled. it was Saturday and i planned on going to the store and she asked if she could come said sure and we spent the whole day together just browsing around town and getting some neat stuff. that night i dreamed of sneaking in her bedroom (her knowing and seeing me of course) and slipping into bed with her and having with her! the dreams made me horny and quite happy :) i think she would say yes to the offer but.. what should i do? she is my step sister after all. it wouldn't be wrong would it? i feel sooo bad and sad for her :( helpz!?