I am so very, very sorry pastafreak. The hardest part is sometimes that they don't understand, but maybe that is not a bad thing; They do understand love and being cared for though.
I have been devastated about my Tilly, I haven't slept all night, with the recriminations, whys and what ifs, but none of that really matters; what matters is she was loved and cared for and didn't suffer at the end. Your Cleo is dearly loved and lucky to have you and she understands that.
I luckily got the strength to make that awful decision not to prolong things, (but she only had one to two days left) and the end was so peaceful, dare I say, an almost a lovely experience for her to go so gently and I have no regrets that it was the right thing to do.
Your heart will be breaking, and nothing you can do will make that go away, as you are obviously a lovely, caring lady. Make the most of your time together. The steroids may help her and give you some more quality time.
I am so sorry and am here for you x