Well, you might try this?
“You’re a smart woman and you’re going to make your own decisions. I’m going to say this now, once, and never mention it again unless you bring it up...I’m deeply concerned his drinking will get worse. As a favor to me, I’m asking you to spend ten minutes reading this link (insert link to Friends And Family of Alcoholics here).
I love you and want only good things for your life. I will support whatever decisions you make.”
If she does read here, at least she will have the information. What she does with it is her choice, yes?
You’re a good mom. Sending you a hug.