Not speaking of Zerelda alone, but women in general, of that time had hard lives. Today, women complain if they don't have a dishwasher, or other modern conveniences.
Sometimes we forget what the lives of these women were like. We can make movies and watch tv shows like, "Little House" and "The Waltons", and even still we are not privy to the actuality of it all.
Zerelda had all of this,then add the Civil War, outlaw sons, a maimed arm, a mentally handicapped husband, one dead son and then another. Yes, I would say she became hard and unfeeling to an extent. A lesser woman probably would have had a breakdown.