Ditter, I am so sorry for your loss - it is so hard to lose a beloved dog, particularly when they are suffering at the end.
A lot of people do not know that atafloxin can be a big problem with peanuts/peanut butter. For some reason, in some seasons, it is a bigger problem than most know.
Maybe it is related to mold? Could your little girl have gotten into moldy tree nuts? Might be worth doing some research -