Hi, as I'm sure you know, isospora is a form of coccidiosis and usually, if one pup from a breeder ALL dogs have it even if they test negative. Therefore, the most important thing you should do is treat your new baby with it, even before she shows any signs. Often, when a tint pup starts showing signs, it has already taken a huge toll on the tiny body. PLEASE BE PROACTIVE. It usually takes at least 7 days for coccidiosis to show signs. The germs for this stay active for at least a month and bleach is the only thing to kill it, but have to leave the bleach on your floor, walls, bedding, dishes, leashes, toys etc, for at least 10 min for it to be effective. I think you will just to keep your baby off the carpets until a month has passed unless you want bleached out rugs though.
As far as giardia goes, all dogs from the breeder probably have this as well. The same kinds of bleach disinfection is necessary. And once again, it can remain in the environment foe at least a month, and your new pup should be treated or it even before showing signs. Stress really can make both these parasites effect the pup harder as well.
I hate to ask, but are you sure the breeder is not a mill? To have a pup die of this probably indicates very poor sanitation on the part of the breeder.
Giardia in Dogs Coccidia - Wikipedia, the free encyclopedia