Finally she got away entirely.

After starting the bunch well ahead, I went after her.
Well, the cow and I ran nearly side by side for as much as half a mile at top speed.

She declined to be headed.

Finally she fell down and was so entirely winded that she could not get up.
"Now, old girl, I've got you!" said I, and set myself to urging her to her feet.
The pony acted somewhat astonished, and suspicious of the job.

Therein he knew a lot more than I did.