Is what the questioner did, taking medication to delay her period in order to perform 'Umrah, correct? And what are the consequences of trimming the hair for the first time after seeing blood? And is what she considered istihada (non-menstrual vaginal bleeding) and her fasting and prayers in the days that followed correct?

If the bleeding stops completely after purification, ghusl (ritual bath), fasting, and prayer become obligatory. Any yellowish or brownish discharge that appears after purification is not considered anything, based on the hadith of Umm Atiyyah. Consequently, the 'Umrah is valid. As for the blood that appears days after taking the pills, if it has the characteristics of menstruation, then it is menstruation. Otherwise, it is irregular bleeding (dam fasad) which does not prevent fasting or prayer, and the opinion of doctors is relied upon in determining its nature.