I'm so sorry for your loss. I could tell from your posts how much you loved her and wanted her to find a good home.
Not to upset you, and this could just be the law student in me, but the circumstances of her death seem very strange. You said she was fine for her previous vet check........You would think if she was acting ill, they would've e-mailed you earlier to see if you had any advice. Also, why are they being so vague with you when you ask questions? I hate to say this.......but I'm wondering if there was not some kind of accident that killed her (like she got stepped on or something). I think you need to get those vet records before you give away one of your pups.