Well, maybe you are reading too much into it. I'd overthink it if I were in your position. But as much as it sucks at some point in life you realize that not everyone will care about you as much as you care for them.
Now you can try to get her to care more about you or you can find someone else to pass the 'best friend' title to.
Now you can try to get her to care more about you or you can find someone else to pass the 'best friend' title to.