What should a wife do if she menstruates before Umrah and there is a possibility that she might purify before returning or not? And is it valid for her to stipulate at the time of Ihram by saying: "O Allah, if a hinderer prevents me, then my place of dissolution is where You have prevented me"?

Menstruation does not prevent a woman from entering into a state of ihram (definition) for Umrah (definition). However, she is not permitted to perform the circumambulation (Tawaf (definition)) and the striving (Sai) until she becomes pure and performs ghusl (definition).

The woman remains in her state of ihram until she becomes pure. She can stipulate at the time of ihram that she will exit from her Umrah if her menstruation does not cease by the time her companions depart.