Good morning and Happy Thanksgiving. Lauren's words are so true, and your feelings for your sweet Sadie are one of deep love. When Sophie was ill (she was 13) and the second opinion vet told me she was in a fragile condition, she looked like a child in Dafur (not fleshy on her body but a little pot belly). She was losing protein and accumulating fluids. I also had difficulty sleeping and silly people would say the same "put her to sleep" or "she is old".
So, don't let anyone tell you differently because she is your beloved friend. The good and positive sign is she is frisky. When she is at the vet, I wouldn't hesitate to call whenever you feel the need to be reassured. Staying there will enable to vet to monitor her blood pressure and etc.
I am sending you this link
http://www.thepetcenter.com/gen/kf.html. Please do not be alarmed. The knot could be an sac of fluid. Take good care and will watch for updates. Try to focus on her today and good health. It is so frightening when they are ill and I will tell you a secret: Sadie is here now, and we are never sure of the future, are we? Hug her and know you have friends in YT who do understand. Write until you feel you have expressed your feelings - Warmly, Deborah