What is the reason for this married woman repeatedly looking at the 'awrah (private parts) of other women, despite her repeated attempts to stop, and how can she definitively escape this sin?

You must lower your gaze from what Allah has forbidden, as Allah Almighty commanded in Surat An-Nur, and as the Messenger of Allah, peace and blessings be upon him, commanded and warned against the consequences of unlawful looking, saying: "Do not follow a glance with another glance, for the first is yours but the second is not." And his saying: "Indeed, the glance is a poisoned arrow from the arrows of Iblis. Whoever leaves it out of fear of Me, I will grant him a faith whose sweetness he will find." Therefore, the sister must lower her gaze from what is forbidden, strive against her self to stay away from wicked websites, and be mindful that Allah is aware of her actions.