Well, I don't think this was a good or smart thing to do.
I can see why she wouldn't want to let her kid drive if they are drinking, but this is mostly humiliating and silly. Also,it feels from that ad that she's getting into a power struggle with her son, parents should not be in that position, it feels to me like she lost all authority (if she ever had any) on her kid and now uses the only authority she still have which is ownership on the car.
I think that if the kid's old enough to drive, he's also old enough to make his own choices about drinking or not and face the consequences of his action (like getting arrested if he's caught DUI) I don't think this serve any purpose aside of humiliating her child. He's still going to drink and probably drive in friends or parents care - so what had been achieved really?
In acting as if her son is still a child, she's preventing him from learning how to be a man.