The caregiver that I hired has already filed for a work permit in her country of residence based on the approval of my job offer from HRSDC. However due to the processing leadtime, she hasn't received her work permit yet and the LMO has already expired. Do I need to renew the LMO now or should I renew it only upon the advise of the visa officer?

Assuming that she sought the work permit prior to the expiration of the LMO, a new LMO or renewal should not be needed.