Medical examination is not a long procedure in Qatar. She has to go only for blood test and Chest X-ray which can be done at the Medical Commission within an hour. To my knowledge it has to be done within a month time provided she is holding a visa for processing the family resident permit.

If she is arriving Qatar on a visit visa, the medical tests has to be finished as soon as she arrive in Qatar because the extension for the visa will be possible only after getting the medical test results. So everyone who comes to Doha on visit or for Resident Permit goes for medical tests on the same week of arrival. Don't waste time for getting impt things like this on right time!