I think you are absolutely right to be concerned the way you are. I didn't start heavy drinking until my early 30s and it snuck up on me like it has your wife. I drank at night after working full time plus OT and taking care of all my household responsibilities. Once in a while my husband would comment I drank too often but it was a source of pride that he couldn't point out anything that was amiss because of it.
He never really confronted me and demand I cut back or quit. If he had I would have gone into full blown defense mode. I knew I was drinking too much but I didn't realize what was happening to me. It was as if I was hypnotized and all I knew was that I had to keep my right to drink no matter what. I snapped out of it but there is no telling when that will be for her. I agree that you need to take care of her son and her husband. Maybe that will wake her up and maybe it won't. Doing nothing is too risky.