First off, what kind of fencing do you have? You might want to consider getting some electric fence to put up in front of whatever you have right now, to deter them from going close to the fencing. It sounds like you have wire fence, which isn't great to start with, so putting up electric fence (hot tape) in front will keep them away from it. Make sure your fencing (if it's wire of any kind) is tight all the time - nothing worse, or more dangerous than loose wire fencing.
If you're sure she's going to try it again (horses tend to) then you need to take some preventative measures to make sure it doesn't!!
Regarding the horse, get the vet out, if nothing else to tell you things are okay... because if they're not, and if she's been infected with something, you need to catch it right away.