Heartbreaking for your friend. I hope, in time, she can be consoled with the fact that she saved her dog by surrendering him. It seems very sad that there is no help available in the form of charity or vet payment plan.
Sorry to hear about your friend. Just thinking is there no way she coukd approach the SPCA and ask if she could pay for the surgery in installment plans? Know the Vet won't allow it. Pressume they will have paid the Vet as part of surrendering him to them? If not could they and accept a payment plan to recoup costs. She could also then take out insurance to avoid a future occurance. Might just be worth a go? At least this way tge poor dog does not get a double whammy, surgery and rescue centre for a period until new owners are found.
I would guess that the RSPCA would have pretty clear policies in relation to this kind of thing. They wouldn’t want to set a precedent that’d lead to people using them in this way to fund vet treatment.