What is the ruling concerning the 'Umrah performed by a woman after she had purified from her menstruation, then she saw red blood after completing the 'Umrah and shortening her hair, and she did not ask about its ruling at that time, knowing that she performed other 'Umrahs and Hajj thereafter?

So long as you have verified your purity, performed ghusl (definition), and completed your Umrah (definition), then your Umrah is valid, and nothing is required of you. The blood you saw after completing the Umrah is of no consequence, because the principle is to attribute every new occurrence to the last possible time it could have occurred. Thus, the blood is considered to have appeared after the Umrah, not during it.