What is the interpretation of a Muslim girl's feeling of sadness, depression, and the approach of death, and what is the remedy?

A Muslim is tested by good and evil, and commanded to be patient in adversity and grateful in prosperity; that is better for him. What has befallen you may be due to shortcomings in acts of worship, so you must follow Allah's commands and avoid His prohibitions, for that leads to inner peace and tranquility of the heart. You must remember Allah and supplicate to Him, remain steadfast on His path, and consistently recite the remembrances (adhkar). Know that life's term and provisions are solely in Allah's hands. We advise you to frequently recite the Quran and ponder its meanings, for in it there is comfort, tranquility, and the dispelling of whispers.