During the run down the fence, if your cow tries to come off it and you are right there, it probably won’t try again. Whatever a cow gets away with once, it will usually try again.
Also try to make the first run down a long one to give you plenty of time to set up your second turn lest you end up with a penalty by not catching it before the corner. It will also take more air out of the beast and show off your ability to rate.
Often the cow forces the rider to have to loop it. After the first turn, if the cow comes off the fence at more than a 30* angle, I’d consider this option though it doesn’t increase the degree of difficulty or your control of the cow, it does usually set you up for a better second turn.
As long as there’s no separation (loss of control), the loop is seldom a penalty. (See the illustration below. The horse is the brown arrow and the cow is the black blob. Please excuse my lack of artistic technique.)