Are you the only one riding her or are the people running her still riding her? If they are, I think you are cruising for a crash. Everything you will achieve will be promptly undone by them.
If you are the only rider, do NOT just pull back on the reins. A horse who wants to go can set themselves against almost any bit and it is hard to affect them. You need to pull back, then release, then pull back, then release. This way the horse cannot set against you.
If that fails, I would use a cavalry or emergency stop.
I almost NEVER use the one rein stop at speed as it can turn the horse making him prone to falling and rolling over the rider.
Again, if other people are "cowboying" this horse (SO bad for such a baby!!!) then you better rethink riding her at all, IMO.