I will add another vote for not allowing kids to show a heifer with a bad attitude. There is absolutely no fun in trying to show an animal that has a bad or even unpredictable attitude. It is always better to be safe than sorry. The only thing I would suggest if you really, really want to have a youngster show this heifer, and that is, try to find someone close to you that has a halter breaking donkey. I have seen some animals with real nasty attitudes turn into puppy dog quiet ones after having to deal with a donkey for awhile. I have no idea what the donkey does, but they seem to be able to change mental issues as well. If your heifer still is agressive after trying this, give up on her before someone gets hurt!
I am still suffering the effects of keeping an unpredictable animal around, even though I was pretty certain his previous owners were wrong about him. I purchased a bull from an older couple who said they did not trust the bull so were sending him to market. He appeared to be very quiet to me, so I purchased him because he was a real good bull for that time. I had absolutely no problems with him during the first year I showed him, and we showed him all over Canada and the US, including Louisville and Denver where he won his class in both shows.He was trucked over 10,000 miles in his first show year alone. He was handled by numerous people and several of them commented that all animals should be this quiet. One day when he was just past 2 years of age, I walked into his pen and slipped a halter on him and he seemed to be very normal... which was almost too quiet. As I led him to another pen, this bull suddenly turned and hit me so hard that he put me completely through the wall of a shed. I don't know why, but I got up, came back through the hole and picked up the halter again and tried to continue to his pen. He hit me again and got me down on the ground. I am pretty certain that if I had not been able to get my fingers into his nose ring, that he would have killed me that day. I felt very little pain until an hour or so afterwards, when the adrenaline quit having its affect in my system! I still have an indent almost an inch deep in the muscle on my upper leg below my hip, where he got his poll against me and then flipped me around( even though this was over 20 years ago now!) He went to slaughter the same day this happened.
I found out after this happened that he had turned on the former owner and knocked him down. He was less than a year old at the time, and they decided they could not trust him anymore. I should have asked more questions when I bought him.