What are the ways to help or advise someone who feels unhappy, a burden on others, and useless?

True happiness is found by a person in faith in God, in remembering Him, in being mindful of Him, and in performing righteous deeds seeking His countenance. This is what makes hearts find tranquility and souls become pure, as Allah Almighty stated: "Those who have believed and whose hearts are assured by the remembrance of Allah. Unquestionably, by the remembrance of Allah hearts are assured," and "Whoever does righteousness, whether male or female, while he is a believer - We will surely cause him to live a good life." Therefore, the questioner is advised to strive in strengthening her faith, to constantly remember Allah, to recite the Qur'an, and to perform good deeds.