The death is not related to the speed. He would be just as dead had she been driving 55 MPH. He is dead because he stepped in front of her truck, not because she was speeding.
Or are you trying to claim that she should be charged because the officer died during the commission of an unrelated crime (speeding)?
Unrelated? He was attempting to stop that vehicle for the reason that she was speeding. How is this unrelated to the incident?