What is the ruling regarding the prayers, fasting, and 'Umrahs performed by the questioner, given that she did not know that "yellow discharge" is considered part of menstruation, and she used to perform ghusl immediately after the cessation of brownish discharge?

Yellowish discharge is menses if it is connected to blood or occurs within the period of one's regular cycle. However, some scholars, such as Sheikh Al-Islam Ibn Taymiyyah, do not consider it menses at all. It is permissible to adopt a weaker opinion after an act has occurred and its rectification would be difficult. Therefore, you are not required to make up the prayers you performed out of ignorance. This also applies to fasting and 'Umrah (definition). If you wish to be cautious, determine the number of prayers you performed without ghusl (definition) and make up what you believe to have been menses, and make up the days of Ramadan (definition) during which you saw the yellowish discharge. As for 'Umrahs, if you performed another 'Umrah after it with proper purification, it would suffice for the previous one. Otherwise, your ruling is like that of someone who circumambulated while menstruating.