Of course, if the only reason DUI charges were ever filed is to keep people from hurting themselves behind the wheel, it would be a different matter. the point of keeping intoxicated folks from operating any means of transportation is to protect not only the person who is intoxicated, but also other people who could be hurt due to the person's negligent behavior. Whether she was on a horse, a motorbike, a bicycle, or in a car is really a moot issue. She was creating a danger to herself and other people on a public and relatively busy road, and deserved what she got.
At least that is the opinion of one person who lost a brother because two idiots did not have sense enough to stay home and do their drinking.