I am not implying that you would harrass this person or them you, but cases have occurred where a member of the donor's family or the recipient have made things very uncomfortable for the other party. It is easy to see how these types of things could be upsetting. But if the OPO says that one party is uncomfortable with it the other party must respect their privacy, even if the intentions are honorable. Some families leave instructions with the OPO not to forward letters, as they do not want to experience the pain of remembering their loved one. Other times the letter may evoke extremely stong feelings that may have a wonderful effect on the donor's family, yet they are unable to respond with words or unsure of what to say.
Every family grieves differently.