Yes, your wife should visit medical commission and inform them that she's applying for visa conversion i.e. from visit to residence visa and pay 100 QAR..Tests wouldn't be done again.
After updating details in their system, receipt will be issued stating medical test for residence visa.
You may go for finger printing the same day...do carry your wife's photograph and her blood group report.
After two or three days, you may visit your nearest Passport and Emigration Service Center alone..but do carry your wife's original passport for visa stamping.
Hope this helps!!