I got married three years ago, and she will not wear the hijab; what is the ruling on that?

A man must advise his wife and strive to encourage her to adhere to the hijab (definition), and to warn her of Allah's threat regarding immodest display (tabarruj); based on the Prophet's (peace be upon him) saying: "Two types of the people of Hell I have not seen. People with whips like the tails of cattle, striking people with them. And women who are clothed yet naked, inclining [to evil] and inclined [to evil], their heads like the humps of leaning camels. They will not enter Paradise nor smell its fragrance, though its fragrance can be smelled from such and such a distance." If the wife does not adhere to the hijab after being advised, then she is considered disobedient (nashiz).