JetMetFan wroteThe opponent needs to be able to take at least one regular step from the moment the screener legally sets the screen.
That's for a stationary defender. Diggins was actually a moving defender, and at the speed she was moving, she probably should have been afforded two steps.
If a blind screen is set on a stationary defender, the defender must be given one normal step to change direction and attempt to avoid contact. If a screen is set on a moving defender, the defender gets a minimum of one step and a maximum of two steps, depending on the speed and distance of the defender.
Bottom line? Illegal screen.