My condolences.
My mom died last month and she was a professional musician, so I played one song that my mom taught me when I was a baby laying under her piano.
"God Bless the Child".
It was certainly well received, as if it were the perfect choice, and I know it was for me because of the meaning.
This is a youtube version of my playing it solo awhile back:
http://www.youtube.com/watch?v=EFQUfFyYubw
Best wishes -