I always try to be careful when answering a question like this. It may seem rather straight forward but if I can not see the situation I am not really sure what happened. Horse behavior is not always simple and straight forward like the operation of a car. There are several reasons that a horse might bite, either each other or your daughter. I would handle them in different ways.
When did the biting occur? I have a stallion and a gelding together and they love to play. They mock fight, rear up, and chase each other. It is a hoot to watch, but in their play they bite each other. I will see little bits of hair missing, normally in winter when the hair is long. This is not something I am going to correct. They are horses acting like horses.
On the other hand I would not tolerate any bulling type of behavior if I was in the pen with them. If I had a horse that was to try and push one horse out of the way, bite or kick at another horse to get to me, or food I am putting out is a big no no. I would "get big" to this horse, or yell, wave my arms, and move into the horse to chase them off. You're saying to the horse, I am bigger and badder than you so you better get out of my way. In a herd that had this behavior typically I would take a whip in with me.
What was happening when your daughter was bit? I got a horse bite the other day, but from my draft horse. It was totally accidental, I didn't even know she really got me until later. My arm was by her chest and she went to nip at a fly and my arm was there. I smacked her chest and told her to "knock it off" I honestly didn't think she got me until later I looked at my arm and I have a little bruise. That was not a meaningful bite, she did not know my arm was in the way, she can't really see her chest now can she. Even still, I will not tolerate a horses teeth on me. Especially from a mouth that could take my whole hand.
The same draft mare will try to mutually groom me when I groom her. This is a typical horse behavior between two horse friends, they will stand head to tail and use their muzzle and teeth to "massage" each other . As I am brushing my mare's wither area, she will try and rub my back or scratch me with her teeth, like mutual grooming that horses do. I do not allow this. As cute as it is I could get really hurt, especially with the little teeth nibble they do to each other.
Now for the issue with your daughter. Were the horses tied or loose when she was bit? Did she have treats on her? Were the horse trying to bully other horses, or were they trying to get something from your daughter? Was she grooming the horse? Catching the horse? Just visiting in the paddock? Each of these situation would be handled differently. If the horses were loose then the getting big and scaring them off is effective, but if there are a lot of horses around your little girl I would be concerned they would spook into or over her (if she is a small child) trying to get away from you "being big." If they horse is tied, then you just want to be care with spooking the horse who may learn to pull back when tied, or be spooky when tied. I normally smack and say, "knock it off."
Is your daughter old enough to be in 4H? She would learn a lot about handling horses in 4H.
You may want to see if you can't get a few books on equine behavior to learn and little more about how a herd works. Think Like a Horse by Cherry Hill, The Ultimate Horse Behavior And Training Book by Linda Tellington-Jones, Horses for Dummies, and Horses Don't Lie: What Horses Teach Us About Our Natural Capacity for Awareness, Confidence, Courage, and Trust by Chris Irwin are some good starts.