https://www.bloomberglaw.com/public/desktop/document/LarsonvPerryetalDocketNo119cv10203DMassJan302019CourtDocket/2?doc_id=X4C1JG8DIN58IVP76AC7631DIMBCourt document with surprisingly clearly written text explaining why:
1) the donor had copyright protection despite lack of publication,
2) the person who wrote stories inspired by the donor's letter was protected by "fair use", and
3) why the donor's sincere belief that it wasn't "fair use" protected them from a defamation countersuit.
Everyone who has every told their donation story should know about this case. Best wishes, all!