We are in the realm of usage and convention here, as opposed to grammar and rules. Needless to say, English has native speakers of various dialects all over the world. Each of those speakers can be speaking their standard dialect perfectly, yet sound quite different from other native speakers.
If a form is correct where it is being spoken, then it is correct.
Her/she is not a common or accepted usage/convention for describing the United States.
Sure it is. Haven't you ever sung "God Bless America"?
Stand beside her, and guide her, through the night with the light from above.
Most countries are referred to in the feminine sense because the Latin noun for earth, or solid ground, is terra firma, which is a feminine noun. That's why it's called Mother Earth, and the ground upon it is "she" or "her."