Is it permissible to go to Jeddah and return to Makkah to complete 'Umrah after menstruation, given that she intended to stipulate a condition upon assuming ihram and doubted the timing of her utterance?

You are not required to stay in Mecca, and there is no harm in you going to Jeddah or elsewhere. The important thing is to avoid the prohibitions of ihram. When you become pure from menstruation, you should return to Mecca and complete your 'Umrah.