One doesn't follow the other. Studying for and becoming a qualified bridge officer doesn't mean that Deanna is competent to operation all the consoles, at all the bridge stations. She tested to be a commander not a systems operator. She like didn't know how to handle ops either. It was more a case of she was the only person on the bridge who wasn't critical where they already were. Riker was hoping that Deanna was intelligent enough to rapidly figure out the basic helm controls. This is similar to the time Captain Kirk ordered Yeoman Rand to take the helm, she was simply standing there. Riker ordered Deanna to get the ship out of orbit, but when we see the ship's exterior again, it is still executing the turn the previous helmsman initiated. Deanna wasn't yet in control, because the ship was still turning and hadn't begun to leave orbit.