I'm so sorry your having to do this,,I know this must be one of the hardest things in your life, but your doing the right thing.
I remember reading about Nova from the moment you got her,,and I guess what woud PEEVE ME OFF, the most is ,,that puppy HAD to have been sick BEFORE you got her. I give the breeder credit for continuing to say she would take her back, BUT I think she should give you your money back or at the very least pay some of those hefty vet bills.
I don't blame you one bit for not wanting a replacement puppy from this breeder. After all this, I wouldn't want a replacement from her either.
The LEAST she could do is offer you your money back, tho I'm sure she doesn't have to.
It will be most interesting to see if the breeder's vets can come to a conclusive diagnosis and what her future holds. Personally, I tend to agree with you, that this dog has had so many weird health problems in her short life, that she is destined to have many more in her future.
don't beat yourself up, you've gone above and beyond,,frankly I would have dragged her butt into court to get my money back.
I hope Nova's problems can be resolved, and hope you get thru this difficult time
diane