My current follower (Serana) kills enemies - those kills are added to my own "Combat Stats" even though I didn't kill them myself...is there any way I can prevent her kills from being added to my own kills?

For example, I currently have "Animals Killed: 0" on my combat stats menu. Serana then kills an animal, and now it says "Animals Killed: 1" on my combat stats menu. Just because she is in my party, I don't believe that I should be claiming her kills - is there somewhere in the Creation Kit that I can change this?

I've tried looking in the CK, as well as searching here and googling, but can't find anything relating to follower kills counting towards the player's total kills.

It's probably because she's set as a player teammate. You could try finding her "follow me" code and commenting out the line that sets her as a teammate, just be wary as that may cause other issues.