Is it permissible to adopt the view of the female doctor who considers any bleeding after the ninth day as istihadah (post-menstrual irregular bleeding) for women, especially given the presence of obsessive doubts about distinguishing purity from menstruation, knowing that the white discharge (al-Qassah al-Bayda’) may be slightly yellowish when placed on a tissue?

The cure for obsessive thoughts is to ignore them. The white discharge is a normal white secretion that is considered ordinary moisture. A slight change in its color is of no consequence, and it does not prevent purification (ṭahārah). So, when the blood stops, along with any yellowish or brownish discharge that was connected to it, then you are purified. If you left prayers at a time when they were obligatory, you must make up the missed prayers because they are a debt upon you.