I am so very very sorry for your loss, but having had rats similar in the past (all rescued) I can understand your concern. Unlike dogs and cats, there is not much that can be done for rats with agressive tendencies. Like we say in the rat fancy, some are just born with a mean streak. There is nothing you can do about it. I fully support your decision, especially with her current health issues. I am sure she is very thankful you have had her this long. Most people would have abandoned her a long time ago. Keep your chin up.