These horns are perfect for your demon or dragon girl.
This product is no longer in stock
These come with a post to insert into the head. You will need to create the holes in the proper spot on the doll's head yourself. If attaching to a bald head, you may need to fill in the gap so they would be flush. Most people will use them on a head with hair so it sits just fine. (See pictures)
Use CA or another adhesive to permantly connect.