They don’t know yet, they are going to do an autopsy, so we may know in a week or so.
I know she battled with mental illness back in the early 80... that’s why I said “ remember me well” , as Lois Lane.. and not the crazy times, so it could have been related to that, suicide, drug or alcohol?
On the bright side, I am pretty sure we can rule out kryptonite, since she was an earthling ;-)