How do you fix a light front end?

Since Sugar is my first young horse, sometimes our "corrective actions" for bad behaviors are more of a let's see if this works experiment.
She's a great horse on the ground, a little wonky still with standing still while tied, but I would say 90% of the time, all four feet stay where I put them. She's a great little horse to lead when no one lets her get away with grabbing a bite to eat here and there, but sometimes she does get worked up. I think a lot of it has to do with the attitude and nervous level of the handler (typically me). I am quick to get nervous, and she usually balances that out because she is not quick to get nervous.
However (you knew that was coming lol), Rally is buddy sour. That is a problem in itself, but when I take Sugar away he runs the fenceline, whirls this way and that, runs in and out of the barn, and whinnies almost constantly. Normally she ignores it, but sometimes lately she gets a little worked up (i guess that means she's buddy sour too??). Say I'm leading her away from the barn (halter and lead) she'll do that head toss thing mares do, and she'll pop up just a little. She did it twice and I growled at her, and she calmed down and walked patiently.
Last night, the perfect storm happened, I had a bad day, she decided to pull this little trick out of her bag and I had enough. She tried to toss her head back and forth, which I corrected with a tug on the the lead and therefore her halter. Then she popped up a little, I growled at her, and she walked a few more steps, then she popped up a little again, and I yanked down and towards myself with the lead. It wasn't a light yank, and I heard the halter snap down on her face. I felt really bad, and I wondered if that was too harsh. I know lots of people say never to yank on the halter, but what are your options from the ground when your horse does this?
 One good thing came out of the halter yanking, she didn't try that again. I did some groundwork with her right then and there, and took her to the round pen, and released her, where she decided to try and run that fence. (I had no lunge line, just a halter and lead)
So, I picked up the whip and sent her off. She chose a fast canter and also chose to buck a few times. I didn't really do anything about the buck. I did not pay attention to her unless she started to cut in. When she started to do a calm trot and drop her head and turn her ear towards me, I praised her with my voice and let the whip drag on the ground. I asked for a walk and she walked (sugar is mostly voice command trained). So I turned her around, and off she went at the almost gallop and bucking...same thing as before. When we were done with that, I did some ground work and turning and backing. She was nice and calm by then, so I took her back towards the barn.
What would you guys have done differently?