Fixing the drinking problem requires acceptance of responsibility, and that goes for our drinking, or someone else's. You require that your GF accept responsibility for her drinking behavior, and responsibility for fixing it. You will support her in any way she chooses as she finds her way, but drinking is no longer acceptable. AA, rehab, detox, counselling, therapy, it doesn't matter, but it is her responsibility to fix this.
There is no anger here, just a simple statement of fact, some new information that she needs to hear. Give her some time to think this over carefully, say an hour or two, and then she needs to give you her answer. She gets one shot at this.
This can work, and I am speaking from my experience. I wish you the best, William.