The wonderful thing about literature is that it is subjective. Opinion questions like these illustrate this truth. Here's what I mean: If you think Mr. Oakhurst is admirable because he is so level-headed and you can prove your claim with quotes from the story, then you are right. If one of your classmates thinks Oakhurst is a jerk for leaving the women at the end and instead thinks Piney is the most admirable because of her innocence and can prove her claim with quotes from the story, then she is right, too. So what I'm offering you is ONLY an opinion.
I admire Mother Shipton the most. Just as her name implies, she is a mother-figure to Piney in their dire time. She selflessly saved her rations for Piney even though it cost her her own life. She didn't even want the credit for doing so, saying
I'm going . . . but don't say anything about it. Don't waken the kids. Take the bundle from under my head and open it. . . .Give 'em to the child.
It's hard to believe such a woman just a few days earlier was banished from a town. Of course, as a single woman on the frontier, her career options were limited; and when the town "experienc[ed] a spasm of virtuous[ness]," she was banished because of her profession of "impropriety." It seems to me that she, like everyone else on the frontier, just did what she had to do to survive. While Mother Shipton could have been bitter toward the judgmental attitudes of society, she instead embraced her maternal instincts and tried to provide hope for the younger Piney.