As hard as this is going to sound, I think I would consider finding a new friend. This one is not trying to be mean, but she has a life to live, as do you.
I'm sure you are the one she calls for everything, stop being there for her every need. When you quit being so available to her, she may then decide that you were indeed what she was looking for.
If that doesn't happen, then you will have 'moved on' and hopefully found someone who appreciates you, and treats you like you deserve, rather than just a best friend.