Is it permissible for a servant to ask for death for fear of falling into sin, especially with intense sexual desire and inability to marry, and is that considered a lack of contentment with Allah's decree?

It is not permissible to wish for death out of fear of falling into sin, and part of the wisdom behind this prohibition is that it implies a lack of contentment with divine decree. Marriage is one of the greatest means of preserving chastity, and one should hasten to it. It is permissible for a woman to seek a righteous husband, provided she adheres to the lawful controls and seeks assistance from trustworthy individuals. If marriage is not facilitated, then she must be patient, avoid lust-inducing stimuli, and frequently supplicate.