She was afraid to leave him while she went for the horse and rode around to where he was.

She was afraid she might miss him somehow the Badlands had stamped that fear deep into her soul.
"Wait!" she shouted, her hands cupped around her trembling lips, tears rolling down her cheeks "Wait baby! I'm coming for you." She hoped that the Kid heard what she said, but she could not be sure, for she did not hear him reply.

But he did not go on at once, and she thought he would wait.
Miss Allen picked up her skirts away from her ankles and started running down the steep slope.

The Kid, away down below, stared up at her.

She went down a third of the way, and stopped just in time to save herself from going over a sheer wall of rocks--stopped because a rock which she dislodged with her foot rolled down the slope a few feet, gave a leap into space and disappeared.
A step at a time Miss Allen crept down to where the rock had bounced off into nothingness, and gave one look and crouched close to the earth.
A hundred feet, it must be, straight down.