Sounds like she wants to be in a relationship with you before doing that sort of thing, whereas you want the 'friends with benefits' sort of thing.
You're going to have to set things straight for her as she'll be a bit confused at the mo - if you're just wanting to mess around then you should tell her, and she probably isn't going to want to just do that.
If you just keep trying to do this without making things clear it will hurt her in the long run, and will definitely jeopardise the friendship.