Here is some data on the topic. It also reports the prison composition by gender for each crime category for comparison. The data for the NCS is from the year 1988. The conclusion, in a generic sense, which follows is that women are underrepresented in prison for a broad spectrum of violent crimes, including murder.
Murder is a particularly tricky issue.
It's hard to tell how much to trust police reports. I think that the bias of the justice system as a whole is best addressed by looking at other crimes where data by the victim is available, and assuming similar biases apply to murder. Unfortunately I don't have the documentation to address this issue as fully as I would like. Men actually recieve greater sentences even when prior records are taken into account. This doesn't even begin to explain the huge difference between the composition of the criminal population and the prison population, however.