YANBU
What a horrible and sad task. I don't blame you for dreading it.
but, it is probably a compliment that your boss has asked you to do it, it means he thinks you have the sensitivity and discretion to handle it.
Please think of it as something you can do for her daughter (even though she won't ever know), to finish off her work affairs properly and sort through her pending cases so that her professionalism is upheld.
Good luck.