You are voicing a lot of anger. That anger is coming from you being frustrated that you cannot control what your mother does when she takes your son out of your presence. You might as well accept that you do not have control of that, and you never will. If you don't trust her judgement about your child's safety - and you have good reason not to - then it is your responsibility to not put your son in her care, or to do so only under limited circumstances . . . like those that do not involve transporting the child.

Your mother grew up in an era when people had much more relaxed ideas about how much beer, before taking the wheel of a car, is too much. In her judgement, what she did was fine, and I doubt you will be able to reprogram her thinking. She demonstrated that she is willing to ignore what you expect and substitute her own judgement, when she feels you are being overly cautious. It is very likely that she will do that again, perhaps in respect to some different issue. Eventually, you may decide that your mother is not a good choice for babysitting. I've known couples who have decided to not allow a particular grandmother (or other relative) to babysit. It's okay to make that decision. It's not okay to go around angry that you can't get someone to have the same judgement as you have. That's simply not going to happen, and you might as well accept the reality of that.