Apparently, she suffered full cardiac arrest this morning.
Murphy was one of those actresses who managed to put together a prolific career without many "starring" roles. She always played a second or third major role very well.
She was great as the voice of Luanne and young Joseph on King of the Hill. Her performance in 8 Mile was excellent. She also had strong performances in such movies as Clueless (her first big break), Sin City, Girl, Interrupted, and Don't Say a Word. She collaborated with legendary DJ Paul Oakenfold on the number one Billboard Dance Club hit, "Faster Kill Pussycat".
I was not aware that she had health issues. It will be very interesting to see what brought this on, as I've never heard of her having any kind of health problems.
While I'm not the biggest fan of "celeb gossip" sites, TMZ usually has good scoops on these things and you can track their updates here.