I might just be drawing this conclusion out of thin air, but it's possible she has something else going on her life that's taking up all of her attention, and she just wants to be left alone, and she didn't know how else to do that besides unfriending you. Ever heard of the INFJ doorslam?
It's too bad her behavior is so confusing. I know that I myself have acted in confusing ways in these sorts of situations. Personally, I have a lot of trouble figuring out what I want. I've read similar things from other INFJs on this board. Sometimes it just takes a lot of time to come to conclusions; it's possible that she was really confused herself and couldn't make up her mind for a really long time. What do you think was going on?