What is the ruling on a woman breaking her fast on a day in Ramadan because she was not certain of her intention to fast, due to her not being sure about the cessation of the yellowish discharge, knowing that a slight yellowish discharge did appear from her on that day? And what is the ruling if it did not appear?

If the yellowish discharge is menstruation, because it is connected to blood or occurs during the usual period, then the woman has the ruling of a menstruating woman until her menstrual bleeding stops.

Fasting on a day where there was doubt about the cessation of blood before dawn is not valid, and it must be made up.