Since English does not have grammatical genders any more, as German still has them, using "she" for inanimate objects is a form of personification (Wikipedia).
Traditionally some nouns are personified more often than others; geographic concepts ("Britain"), emotions ("Jealousy"), and vehicles ("the Lusitania") are among the things more often personified as "she". Personification is a prominent rhetorical device that should only be used when a writer is prepared to draw some attention to his language, because it is not the neutral way to refer to inanimate objects (which is "it").
[Edited:] The reason why some nouns are personified more often than others is probably tradition, in addition to a feeling that they share more characteristics with persons. A ship is an elegant thing that is lovingly cared for by its captain; a country is what has brought forth its people like a mother; an emotion is an important thing that we sometimes curse but could not live without, and it can have the power to make us do both bad and good things.