On weight of evidence but without knowing who the breeder is, I'd suspect she will simply pts. She may be right to take that approach -- if this is SM, a puppy this young showing these symptoms would likely be severely affected. But the sudden interest in replacement only came when financial support was asked for. That to me, says volumes.
If the pup has severe SM, the only real medium to long term option for the puppy for anything but short term palliative care would probably be surgery, which is expensive.
Given the choice, the better option may be to take a replacement puppy -- however if her dogs are closely related and she has scanned none of them, a replacement especially a sibling would be likely, a high risk.
All of these are very difficult decisions to take and a burden for anyone. Jo if you want, PM me the info on the breeder and if I know who they are or the kind of breeding set-up they have, it may be easier to say to work with the breeder.