I am so sorry that it looks like her time, she is so incredibly lucky to have had a mum like you though, who has done so much to keep her happy and healthy, and I know you will do whatever is right for her tomorrow, not all cats are that lucky. It really isn't an easy position to be in though, we are all here for you if you need to talk, sadly the majority of us know what you are going through. At least by choosing, you will know that she has gone peacefully, and with someone who loves her so much with her, rather than having to go through pain and suffering.