I drank like a fish in the military. As did most of us at my paygrade. And since I'm 1/2 scottish and 1/2 norweigian, my tolerance was *high*. Dropping a grand in the French Quarter on alcohol in one weekend was the average. Or a 5th a day + beer during normal circumstances.
Nowadays I might drink 3 or 4 martinis in a night, or split a couple of bottles of wine with friends over the course of an evening *once every few months*. In Italy I have wine with lunch. In the US I don't. When I have housguests that love to cook I drink every night while cooking (a glass of wine while cooking is one of my favorite things). When I'm taking meds for my knees I don't drink at all. Ditto with my Islamic friends, instead of drinking alcohol I smoke or drink coffee. I adjust my drinking to suit the circumstance.
Most normal people (as in non-alcoholics) go through phases with their drinking. The person who decides off the bat that they don't like alcohol and so almost never drink, and the person who gets "stuck" in an abusive phase that then turns into alcoholism are both the RARE people. For the rest of us, our phases teach us our limits. They teach us what we enjoy, what is going to be painful the next day (personally I've only ever been hungover 4 times in my life... I'm one of those annoyingly perky people after I drink, even though regularly I am NOT a morning person... after a night of drinking I'm up super early cleaning and exercising and feeling grand... go figure), anyhow... our phases teach us.
You're right, no one decides to become an alcoholic, but MOST people enjoy drinking with their friends. There is no reason to stop unless it's causing a problem. Most people experience problems with their drinking. And they learn from those problems. A key difference between "normies" and alcholics is that "normies" learn, while alcoholics keep doing the same things over and over expecting different results. She'll never learn her own limits unless she tests them.
I knew when I was drinking like a fish that it was a strong possibility that I was an alcoholic. It runs in my family as well. But when circumstances changed, so did I. COULD I become an alcoholic one day? Sure. Am I now? Nope. Was I then? Nope. I was abusing it, certainly, but I changed how I drank. I didn't know until after I was able to drink moderately whether or not I was an alcoholic. A key component in alcoholism is NOT being able to change.