What is a dime or nickel piece dated 1891 with the letter V on the back and the head of a woman on the front?

This would be a Liberty Nickel, also called a "V" nickel. They were minted from 1883 to 1912 (and 5 dated 1913). Values range from about 10 cents for one worn almost beyond recognition to about $2 Million (for one of those 1913's).