User blog comment:Xano501.ben/A reason why Ahri can hear Sona/@comment-5331854-20130725160046

Another good reason could be that her first "victim", a "robed man encircled by a waning field of magic", was actually a dying Summoner. And since Summoners can hear Sona with the help of a magical connection, it wouldn't be out of the blue for Ahri to be able to hear Sona, too. Could actually be empowered by her gumiho-heritage, if you want, because she doesn't need to summon Sona to hear her thoughts.

Two birds with one stone.