So, there's this girl I like............

[Iggy]

I can't really say what she is thinking as I don't know her. But I know when I was in high school and had just broken up with a serious (relatively) boyfriend it was very uncomfortable when a guy friend wrote me a letter saying he liked me. I didn't want anything serious and since we were friends I couldn't see us just having a fling, which is all I wanted. She might think that since she likes you as a person, any relationship with you would get serious and she isn't ready for that. If you make her think that she owes you something (even if you are kidding) then that would be enough for her to run the other way. She probably thinks it would be too awkward to say "thank you" to you at the moment. Or she thinks if she does say "thank you" it means she likes you more than she does and you will expect more from the friendship.