Final answer:
The mother likely wants to distract her child to prevent her from becoming upset and preserve her innocence, hence option C: to keep the girl from crying with her, seems the most plausible explanation. Therefore, the correct option is C.
Step-by-step explanation:
The mother in the passage from an autobiography of a Yankton Sioux girl likely asks her child to run when she catches her crying because option C: to keep the girl from crying with her is the most plausible reason. She wants to protect her daughter from the pain and sorrow that she herself feels upon remembering something sad associated with going to the river for water. By asking her child to run, she distracts her and prevents her from becoming upset, thus sparing her from the burden of adult emotions and preserving her childhood innocence for a little longer.