Some horses, especially young ones, need to get the energy out on the lunge line before a ride. It's safer for you, and creates an atmosphere where you don't have to discipline her and start a fight (as it would u/s).
Its up to you what you want to accomplish on the lunge line. Once she is a little older/out of this "stage" you will proably have less issues on the lunge line. You can also verbally reprimand her when she bucks/etc... "EH EH EH! NO!" usually works well. And then a praise when she settles works well too.
If you want to use the lunging time as a training time, then get after her for the behavior. If you want to more or less get out the sillies before you ride, then don't worry too much about it.
I doubt it is agression toward you, it sounds like she's just letting loose a little.
As far as her legs go, as long as you keep her on a big circle (at least 20m) she should be fine. If she is really racing around and being silly to the point where she's losing her footing, then it may be a problem. Try lunging with side reins to encourage her to balance herself better.
Also, polo wraps or some sort of boots will give her some added protection when she's being silly.
If it's only lasting a few minutes I wouldn't worry too much about it, just keep the circle big. They aren't quite as fragile as we sometimes think :)
"The white horse moved like a dancer, which is not surprising: a horse is a beautiful animal, but it is perhaps most remarkable because it moves as if it always hears music."