How is 5 days a long time for a breeder to consider a refund? I'd think it's short if anything. I could totally see getting a ball python, looking it over once and then trying to leave it alone in it's enclosure for at least a week to let it get acclimated. I kind of feel like it's a pretty low likelyhood that the buyer had any wrongdoing. I mean what could an owner do in 5 days that would be their fault and cause the death of an animal? I'd figure most thing would be visible by just seeing a picture of the body. If I sold a snake and it died within 5 days I'd probably ask for a picture(s) to ensure that physical harm didn't happen and that it was the snake I sold, and then issue a refund.
Of course though it doesn't matter what anyone else would or would not do, I'd say the best bet is to take what they'd give you and just move on. I'd agree with the post on BOI and that the snake shouldn't have been purchased. I know the buyer was misled, but if I was buying a snake and I got one that was vastly different weight, then I'd be talking to the seller asap.
Just out of curiosity, why didn't she complain or try for a refund in the first place?