Writing about someone is particular is always a hard write. You did a good job.
While there might be some nits.... it is what it is....that's probably the best I can say.... I hate to comment on a song that is so emotionally close to the writer. Mostly I'd say some of the phrasing... the groove and how you work the rhythm pattern in a few places felt a little awkward to me... but that could also be just my personal preference.
A friend of mine also died from cancer after a battle of many years... I wrote a song about him and included mentions of some of his friends..... you may have seen it when I posted it back in August.... if not:
http://www.youtube.com/watch?v=5DmLXESjGWs as in all works like this it was a labor of love and I just wanted to honor my friend's memory.
I think your song accomplishes the same goal. Good job.