The Silent Invasion: The Change Triology 1

It's 2027 and the human race is dying. Plants, animals and humans have been infected by spores from space and become part of a vast alien intelligence. When 16-year-old Callie discovers her little sister Gracie has been infected, she flees with Gracie to the Zone to avoid termination by the ruthless officers of Quarantine. What Callie finds in the Zone will alter her irrevocably, and send her on a journey to the stars and beyond.