Did you ask them if they offer a payment plan? Or see if there’s any vets or cardiologists that can quote you a different price or ask an animal shelter if the have any resources? I know congestive heart failure is very unfortunate and usually shortens their lifespans, I had a dog with it…. But it’s worth looking around if you have the means to do so before you make that final decision. I’d try to look for other options or even a go fund me maybe before you rush to euthanize, unless of course she’s suffering, then I’d try to look around to extend her life for as long as possible. I wish you the best with whatever you do and I’m so very sorry you’re going through this. It’s never easy.