I spoke to her and she said that even though she was on the train, if she was at home she might never have known because she could have been in another room. Then she never would have known what happened and could have just found him. At least this way she was with him and could hug him and tell him she loved him. Only minutes before she took a picture of all three of them because they looked so happy, all snuggled up together in the carry case.
I think it was a heart attack now I think about the way she describes it. Poor little boy, he was so young, only two. I'm so glad I went into the pet shop that day. I'm so glad I asked about his teeth. I'm so glad I decided to take him and get him the vet treatment, I'm so glad my vets let me put it on a tab as I had no money and I'm so glad my sister adopted him. He couldn't have been with anyone better.
He was so much smaller than his litter mate, perhaps there was always something wrong inside. He was such a wonderful character, full of so much love, mischief and happiness and was loved by everyone who met him.
I will miss him, but I know my sister will miss him more.
Thank you everyone who's replied. I told her about the thread and she wants to read it later, I know all your replies will mean a lot to her.