She did the right thing IMO, although it’s not an easy decision to live with.
Many years ago I called the cops on a well known (retired) tv presenter. He and his friend came into our pub once a week and always drank quite a lot. A member of staff coming in moments after they’d left one day asked how much he’d had to drink, since they’d just spotted him getting into his car.
Next time he was in, I followed him out and sure enough, he jumped in his car. He’d had 8 pints.
I told my boss, we deliberated for about 10 seconds, then called the police. He never came back and I don’t know what happened after that.
I feel bad, but not as bad as I would have felt if he ended up knocking someone down, which, when you are continually drinking 8 pints and then jumping in the car, is fairly likely.