She's not being fair at ALL. It's one thing to cuddle up on the couch with a friend of the opposite gender if you both know all you want is friendship. It's entirely another to ask someone you KNOW has feelings for you to spoon with you all night when you also know you DON'T have feelings for them- or at least aren't willing to take it further than friendship.
I'd say there's one of two scenarios at play here:
1)She enjoys the attention she gets from you as a friend, likes the comfort of being able to call you, cuddle with you, and have you hold her when she's feeling lonely or down. But she has no real interest in pursuing it further than that- she might enjoy your company and even have some attraction to you, but in general, she's not interested, she's just using you when it's convenient...
2) She might have real feelings for you that she didn't before but isn't sure how to tell you because she rejected you before.
Either way- you need to have a straight up conversation with her. Tell her that you guys can be friends without the physical stuff that crosses the line of friendship or you can try being a couple but you can't handle her messing with your emotions by being JUST your friend yet inviting you to sleep in her bed and spoon with her. At this point, it's got to be either one or the other. What she's doing shows a lack of consideration for you and your feelings which isn't acceptable from a friend OR a potential girlfriend. If she can't handle this, then I'd say you need to keep your distance from her.