Deep,
If you should get lucky enough to attempt to give the letter to one of her kin, be prepared for anything in the spectrum of emotions. Some examples:
1. They will hang up on you without getting into a conversation.
2. They will deny you have such an item in its original form.
3. They will ask you, sarcastically, how much to you want for the letter?
4. They will ask to see a copy of the letter by Email before deciding if they want the original.
5. They will hesitate in their response if the letter triggers a deep reaction;or if they doubt your stated intent.
6. They will gladly talk to you about the addressee and ask how you came into possession of the letter.
7. They will say they are not interested in receiving it; even after you gave them the backstory.
If they say they are not interested, ask what other kin might be interested.
Personally, I'd open the letter only with the intent to get other names and addresses, etc.
Don.....
Don.