my garters cause of death?

[BUSHSNAKE]

13 years old? i say old age is a possibility

[chris-uk]

13 years old? i say old age is a possibility

I'm with Bushsnake. If there was no sign of any cause it's likely to be old age. 13 years is a good innings. And it sounds like you did what anyone else would have done. I don't know whether the bad shed is a sign that she was loosing strength or something else was wrong.
I'm sorry for your loss.