Is the 'Umrah performed by the questioner valid, given that she entered into ihram and stipulated while she was menstruating, then bathed and performed the rituals after the cessation of bleeding, and before seeing the white discharge, with the presence of satanic whispers regarding the validity of her purity during that 'Umrah?

It appears that purity was attained by the cessation of blood, and the discharge that appeared after the circumambulation (Tawaf) may have been due to exertion. Purity is a condition for Tawaf only, not for Sa'i (the ritual walking between Safa and Marwah). You should have verified your purity by observing the white discharge (al-Qassah al-Bayda') or complete dryness. Since four years have passed and you are afflicted with obsessive doubts (waswasah), rely on the dominant assumption that you attained purity before Tawaf.

If a woman stipulates a condition upon entering Ihram (the state of ritual consecration) and does not complete her 'Umrah due to menstruation, then there is nothing upon her. This means that your 'Umrah was not valid, and there is no obligation upon you concerning it, due to your stipulation.