she usually refers to boats because sailers used to be only men and they thought “there has to be one woman on this ship on this long journey, so why not make it the ship”. i often hear it refer to countries as well because the leaders of countries used to be mainly men, and when you became a leader of a country, you symbolically married it. cars are often reffered to as female because girls back in the day were possessions, so a car and a woman could be related.