What did Charles and Hal do when Mercedes did not follow the sled?

When Mercedes refused to follow the sled, Charles and Hal decided to move on, leaving her sitting in the snow. Thet traveled three miles before turning around and go back to get her.

On one occasion they took her off the sled by main strength. They never did it again. She let her legs go limp like a spoiled child, and sat down on the trail. They went on their way, but she did not move. After they had traveled three miles they unloaded the sled, came back for her, and by main strength put her on the sled again.