Mary, I do feel your pain, I think most of us have had to let a beloved furbabe go over the years, it never gets any easier, but you did all you could for Kitty and her Sister. Please just believe you did everything you could for them both and they knew they were properly loved at the end.
There will be another cat to fill your heart again. Can't remember who said, and may be paraphrasing, but you don't love the ones you have lost any less, your heart just expands. (Sure it was put far more elegantly than that),
You take care, Sweet, and if you need anything just call or pm me.
Paula xxx