I'm so sorry for your loss, BlueBetta. Sarah was a beautiful girl with gorgeous coloring and great personality (lol, chameleon fish). The two of you put up a great fight against whatever she had but in the end, you did the right thing by ending her suffering. It's hard to say goodbye to your friend but I'm glad Coke is helping you. Cats can always sense emotions and will react to them. When I bury my fish, my one cat Mo always comes with me and sits nearby while I dig the grave. It makes it easier to say goodbye and maybe that's what Coke is trying to do for you, make it easier.
My thoughts are with you. *hugs*
Edit: Coke is adorable! What a cutie kitty!