I'm sorry to say, but once girls make a decision like that, they stick with it. It's just how girls are. Nothing you do or say will change her mind.. nothing! The only advice I can give is to let her go. You said yourself, "she doesn't know." If she was into you, she would say that it would go further. You basically asked her to be your girl friend in a way and she rejected you. She was being nice I'm afraid. If she was really into you she would have let you know, trust me.
It's pretty much awkward now. It's like asking for a kiss. "Can I kiss you?" "Ummm... I don't think I'm ready." That just means she wants to be friends. "Do you think it will go any further?" "Ummmm.. I don't know... it's hard to figure out right now." That means no. Girls like to be nice to keep the guy from freaking out on her.
I will do my best to reply with an educated, humble and honest answer. Ultimately, it is up to you whether you want to listen to my advice or ignore it completely. Sometimes, my advice may be wrong; occasionally, it will be right. Regardless, I want to do my best to give people answers they are seeking.