Why is it be natural for Betty Darr to come up in Ralston's mind during his entrapment?

Betty Darr is a family friend who is paralyzed from polio but has a positive outlook on life. Her optimism is an influence in Ralston's life, getting him to appreciate many things, such as a beautiful sunset. Since amputation is one of Ralston's options, it is natural for Ralston to think of Betty Darr.