Goodbye Stranger - Rebecca Stead

Bridge has always been a bit of an oddball, but since she recovered from a serious accident, she's found fitting in with her friends increasingly hard. Tab and Em are getting cooler and better and they don't get why she insists on wearing novelty cat ears every day. Bridge just thinks they look good. It's getting harder to keep their promise of no fights, especially when they start keeping secrets from each other.

Sherm wants to get to know Bridge better. But he’s hiding the anger he feels at his grandfather for walking out.
And then there is another girl, who is struggling with an altogether more serious set of friendship troubles...