'Dear Casey'

'Dear Kara,
You used to be so different from now, what happened? Are you okay?'
Kara and Casey have never met, yet they are closer than anyone, practically best friends. Their emails and letters are consistent and it's the least to say that they're each other's rock, falling on each other for answers, for help, for somewhere to vent.
But when Kara's emails get less consistent and Casey is left clueless, what would Casey do to save the girl he has never met?