That was never my thought, but I was trying to think of the most outrageous answer and all I came up with was that the man ended up being her sister that she didn't know about or meet until the funeral. She found out that this "man" used to be a woman, and that woman was her sister and she killed he/she out of disgust.
I think too much.
Only working in this industry would I think about the "sex change" factor.