Cee Cee has decided to across Rainbow Bridge

Monday, my sweet ole girl decided to join her older sister across Rainbow Bridge.  Hubby said she had her allotted cooky, came to him for her back scratching as always but seemed a little out of breath.  He emailed me at work to tell me so I asked my boss if I could leave which was no problem, so I could take her to the vets.
Jim said she wanted outside, so she and the other two went out, he came in for a minute and then spotted her laying down on her side.  When I got home, she had passed quietly.  Our vet figured it was either her heart or possibly a stroke, but assured me this was not diabetes related.
She was doing so well numbers wise, and even if we thought something might have been wrong couple days earlier, the vet said it would not have made a difference, especially with the heart or a stroke.
Our rest of the crew know something is wrong, they know their big sister is not around but of course can't comprehend this