@Oman Ra,
I think you went to the nuclear option waaaayyy too quickly.
I agree that this was a big offense, but once you had taken away all of her privileges for the remainder of the school year and had threatened her with a spanking, you really didn't have anywhere else to go, and she knew it. Hence continuing to misbehave (and couple this with the fact that a child undergoing a temper tantrum isn't exactly behaving rationally to begin with), she had absolutely nothing whatsoever to lose by continuing to disobey you. And she had a lot to lose by being obedient. Never mind that she was guilty - she isn't registering that.
Maybe next time, a few ideas -
* calm down. Someone's got to be rational during these episodes. That person, most of the time, has got to be you, the parent.
* don't be passive-aggressive, expecting her to own up to the drinking. Instead, you can be a lot more open about it, e. g.
I smell beer on your breath. Are you sure you don't want to tell me that you had any? Lying to me about this is only going to make things worse.
* think about, and use, a step system of punishments. You don't need to start at step #1 but you shouldn't be starting at step #50, either. Just, have a place to go (and something for her to lose) if she continues to be defiant.
* let her scream her head off if she's going to throw a tantrum. Just ignore her, and read the newspaper or whatever. She is getting a rise out of you by doing that, so don't give her the satisfaction.