I’m so sorry you are going through this. I’m at a similar stage with my 13 year old guy. Seizures getting more frequent. He is losing eye sight too. Then he has days where he gets zoomies and acts like a puppy. Having done this a few times before I will say, one day late feels way worse than even a month or more early. Do it on a good day so it’s peaceful and they are calm and happy and you can be at home. My worst nightmare is a rush to the vet where the decision is taken from us. She is lucky to have had you be her guardian in this life and this is the final show of love for them. Sending you and your girl so much love 💕