I wouldn't worry about it honestly. S...tuff happens and its more likely to happen with horses, plus green unconfident riders. Luckily he wasn't hurt and hopefully he wasn't too badly shaken, but when things happen you buck up and try again. Its not the end of the world to fall off a horse.
Nor would I say your horse is bad. The same sensitivity that makes her ride so nice for youis pprobably what sent her running off with him. She was doing what she knew or thought she should in that moment in time.
It's too late to worry about it now. Put your frustration behind you and keep this as a funny story to tell your friends :)
Posted via Mobile Device