Gator,
First and foremost, welcome. You are in the right place among good people.
Your thread sparks memories in me but also regret in that I wish I'd have been as smart as you are to see the signs as soon as you have. Be thankful that just a year in, you are realizing this.
Many in this thread think your ex was hiding her drinking. That may not necessarily be the case though I would think, given what you described, it is safe to assume she is least drinking more than you think she is when you are NOT watching.
Problem drinkers / alcoholics (we don't really use labels around here, a problem is a problem) come in all shapes and sizes. Many of them, my ex included, can have a perfectly normal day without alcohol at all. They can also quite often accompany you out to a nice dinner, have a beer or two, or a glass or wine or two, go home with you, watch a movie, go to bed.
What many people around here refer to as "white knuckling" is when someone who tends to enjoy binge drinking decides to abstain or moderate the drinking on their own. In most cases, especially when they are not hung over from a binge, they are trying to fight the urges inside to drink more and more. My ex's solution was always to go to sleep if she had a couple beers and the party was over. Had I dangled a six pack in front of her after a "2 beer dinner", she'd have happily stayed up until it was gone.
You may have entertained your girlfriend by drinking with her, as that is a normal thing to do especially in a new relationship when you are getting to know one another. Nothing wrong with it. It's when you start seeing the signs, like you have cited with her family and friends, the behavior that takes place when you are not present, when the red flags start to go up. You realized this quickly and were right to ask questions. Her responses of anger and defensiveness were typical responses of a person with a drinking problem. A "normal drinker" doesn't respond with hostility when a loved one questions their drinking. They would respond with concern. A problem drinker responds with anger and hostility. Very common trait, very easy to spot.
I realized that when I was home, she was "white knuckling" as much as she could, and eventually there would be days where she would just break and have to go on a bender in the house, in front of me. Not sure if you got there , but was likely going to happen from the sound of it. Or, she would have just started disappearing more and more, with her friends, when the weekends come, it's party time, and you were not interested in getting hammered with her. This is the life you have saved yourself from.
Rest assured, you had no control or cause of her drinking, did not drive her to drink, and your questions about her levels of excessive drinking had nothing to do with the fact she is binge drinking to blackout levels. Those decisions were hers and hers alone.
txjeepguy's case is quite extreme but a frightening picture of what can happen to a guy with a girlfriend with an escalating drinking problem. Find his main thread and read it if you have time. He's also a great model for composure in an insane situation such as this.
Feel free to seek out my threads as well, and PM me if I can be of any support. I know what it is like to remember them in their sober/good times and it tempts you to allow the bad behavior. Most will say things like they will stop, etc, to get you back/keep you in their lives, but in my experience, and all the stories I have read here, any promises to quit are short-lived, if at all. And promises to "moderate / cut down" are pretty much a 100% failure.
Keep reading, keep learning, you will find the way through this.