British singer Laura Critchley co-wrote and sang a tribute to Karen, "Superstar", on her 2007 album Sometimes. I just found it on YouTube as part of a fan tribute to some young man named Lee Mead (not sure who he is). But the song is quite good. Check it out.
http://www.youtube.com/watch?v=36igQGkCfQw
http://www.youtube.com/watch?v=36igQGkCfQw