What is the ruling on someone disliking their grandmother (their mother's mother), despite smiling and laughing with her when necessary?

The general principle is that a Muslim should not hate any Muslim, especially one's parents. As for hating the grandmother's actions, if this is not accompanied by any mistreatment of her, it is not considered an act of disobedience (to parents). If her actions are sinful, then she should be advised gently. If she does not respond, then one should supplicate for her and seek forgiveness for her. Grandfathers are like fathers and grandmothers are like mothers in terms of dutifulness.