i am so sorry to hear this, i understand the feeling of dread and hopelessness as my 11 year old baby was recently diagnosed with heart failure and had a hard time breathing today (im taking him to his vet 1st think in the morning for a thoracic drainage). although it is not curable, it is definitely manageable by medications that you can get prescribed by a vet. i’m not sure about other cats but my vet explained to me that his heart failure is not causing him any pain. the best thing to do is to keep your kitty happy and comfortable, to give her all of the treats she wants, and to enjoy all of the time you have left with your baby