the OP was intouch with the seller, and maybe it would have been better
if he didn't process the film and offer her up the negatives or prints ...
unfortunately he processed it already .. but the seller
was nearby ....
after a few days thinking about it,
i spoke to hastily ...
rather than throw the film out i suggest
MAIL her back the negatives with a note saying that
knowing it was difficult to have b/w film processed i had them processed ...
i only suggested that he throw it out after the seller expressed no interest
in it, ( spam filter ? ) ... after repeated attempts by the OP.
And when you don't, it says something about you.
... yes, as I indicated: within reasonable limits. As far as going to extraordinary measures, I'll leave that for some saint... whoever he may be. (insert "halo" smilie here)
While legally the film may belong to the buyer, I suspect copyright stays with the original photographer.
Ethically, if I had contact info for the owner, I'd return it undeveloped.
As a coincidence I happen to have a roll of undeveloped film, from a prior owner, now.
I discovered the film in a camera that I have owned for over 25 years. (I can procrastinate with the best of them.)
I probably purchased the camera at a flea market in the early to mid 80's. While curious as to what might be on there, and whether or not the old B&W film still holds anything, I think I will just stick the exposed band on it, and leave it for display that way.