Tell that to Terri Schivo.
It's an awful law, and physicians should have no part in helping someone to kill themselves.
That said, I do not see where in the Constitution the federal government derives authority to overturn this law. I suspect, though, that this was an outcome-based decision on both sides. The Supreme Court is pretty much a political body these days...kind of a Super-Senate. I'll have to read the decision and dissent to see for sure.
The proper thing to do is to get the voters to undo this mess. They're the ones who voted it in. Personally, I voted against it, as it was and is an awful idea.
Can't. She "decided" she wanted to be tortured to death.