Is it obligatory to perform ghusl and make up prayers for someone who saw a viscous white discharge after her period ended, and doubted whether it was a white discharge (qassah bayda) or madhy (prostatic fluid/pre-ejaculatory fluid), knowing that she performed ghusl and prayed after seeing it?

Purity from menstruation occurs through one of two signs: dryness (al-jufūf) or the white discharge (al-qaṣṣah al-bayḍāʾ). Whichever of these occurs first signifies purity. If a woman observes dryness and no blood appears thereafter, she has become pure, and nothing further is required of her. What the questioner most likely saw was the white discharge. Whoever is uncertain about what is discharged may choose and assign to it the ruling they wish. Consequently, she is not required to repeat the ghusl (ritual bath) nor make up the prayers. It is recommended to ignore and turn away from obsessive thoughts (waswās).