It's really not that yikes-y. We are talking the Great Depression era after all, and she was basically voluntold by her father to help care for the old dying man, in return since he had no money to pay her, they could get married and she could claim his benefits from being in the civil war. During that time, that amount of money could be everything to someone. They kept the marriage a secret, didn't live together, and to my knowledge she never even bothered taking advantage of the benefits after he died

There are still 12 states in the US where there is NO minimum age for marriage, and most states are okay with 17 and under. All requiring parental consent obviously. Now that's pretty yikes