Even if you're drunk, you're still held responsible for what you do. You crash your car while drunk, you get a DUI and you have to pay/work it off. You kill somebody while drunk, you are pinned for second degree murder. You beat your wife when you're drunk, you are pinned with domestic violence. See the trend here? Just being drunk doesn't mean it's not your fault. Downing a mug doesn't release you from responsibility or culpability for your actions when you're intoxicated. If a girl uses alcohol as an excuse, or shimmies of responsiblity for what she did while drunk, you probably wouldn't want to marry her. She probably has issues of her own, and you don't want to be around that.
Well, addressing what your girlfriend told you. This is typical alcoholic/addiction behavior. She continues even in the face of circumstances, and refuses to take responsibility. I say dump her and go find somebody responsible that can take care of herself as well as you.
-Damian