Either do what she asks and lie with her, or be firm and don't lie with her ,its in your hands , by giving in to her you are enabling the behavior. Go to her room when she goes to bed, read her some stories , leave a side light on if she wants it, leave the room , if she comes out tell her to go back.Do not lie down with her or all you are doing is giving mixed messages .Has she always done this, have you always lain on the bed or is this something that just appeared .?