My 11 year old daughter's mare is a finished barrel horse. She uses her for performance 4-H (WP, Western Eq, showmanship, arena trail, Eng Pleasure, English Eq), and places, as well as runs respectable time in barrel jackpots. She also shows the horse in reining, where she always places, and is also using her to compete in extreme trail competitions.
For fun, she puts hundreds of miles of trails on her, and chase cows too. A good horse CAN do it all. But, a good horse is usually going to cost you...a lot!
My daughter has a bit that she uses for barrel races, a curb and snaffle for schooling, that she uses most of the time, and for show she uses a different bit, that she only uses 1-2 times before a show as a reminder. Truthfully, there is one bit my daughter could use on her all the time, and she would be fine.
All that being said, no one else can do much on the horse. She's so attached to my daughter and her riding style, that most people can't get her to do anything. But, as a mom, I don't worry much about the 2 of them together.