When she breaks gait I do the loud "Aeh Aeh!" and a sharp jerk or two, and she comes down. Also when she picks up the wrong lead.
When I have one break gait, I always bring them to a complete "whoa" very firmly. Then start them right back up, and always using "easy" for awhile. Once they have made two complete circles in the correct gait, I whoa them give them a pat, let them stand then try again. I don't make them go for great lengths at a time when they are going correctly. Give them a reward pat (actually I think the whoaing is more reward to them then the pat) fairly quickly. I think that helps them connect what you are asking of them.
If they have broken gait, and get whoaed, there is no pat and no length of time for them to stand, just whoa, start again quickly.
Becky