The question: How do I know when to let her go? is a tough one. I couldn't even answer it with my cat I had put down back in July. But the alternative was giving him sub-q fluids for the rest of his life that weren't even doing any good.

My mom had a min-pin that lived to be 17 1/2 years old. She finally had to make that decision and she actually procrastinated on it for almost a year. Her thought was, he is still eating and pottying just fine (even though he couldn't hold his bladder all day and she had to wash the bathroom rug every night). He was going blind and deaf. He eventually was running into things and began to not be able to walk very well. He was SUPER skinny but still ate good. My mom had to realize all by herself that his quality of life was not as it should be anymore.

Just from what you've posted about Casey it doesn't seem like she's to that stage yet. But I do not live with her, so you have to make that judgement call. Trust me, it is not easy. If you are lucky, Casey will let you know when it's time. My Taz did not do that with me.

I will keep you and Casey in my thoughts.