You Have done the right thing,confronting your Mum about drink driving,and can only hope that it will have the desired outcome. It may be a case of how much of a drinker she is,ie a light drinker,or of an alcoholic type,as in how she might be able to stop drinking.
You just have to confront drink drivers,but sometimes it just doesn't have any effect on them, they come up with any old stupid replies.or get angry with you,and stop communicating.
Years ago,I had experience of a drink driver, he was my partner at the time. He was an alcoholic,but continued to drive about 6 miles to his work everyday. I eventually found out,that he was drinking a large glass of neat vodka in the mornings, and no breakfast. and discovered that he had another small bottle of vodka in his work bag most days.
I informed the police about this, gave them the car reg etc, he had a large distinctive car,and his journey to work,was on a very busy road,going through a small town,with children going to school ,and early morning shoppers etc.
The police never did take any action at all. But fortunately,he lost his job later, and he then spiralled into very bad moods, more heavy drinking, and eventually the drink ended his life in a very bad way.
Sorry this has all been so morbid, but has reminded me of my fears in those days, as in him maybe going out of control when driving, and mowing down some children going to school.