if u got her family visa before she complet 90 days in qatar under visit visa then she needs only to visit medical to convert it from visit to family visa and if she complet 90 days then she will have to make the medical from beginning.
IlikeQL, for visa extention once ure wife comes to qatar and before she complet one month better take her after she spends 1 week here to medical commission she will have to carry passport visa copy and debit or credit card to pay fees (100QR). next day or after 2 days u will receive an sms saying her medical is ok or nt ok, once its ok go to immigration passport with visa and debit or credit card to pay 200 Qr. for each month stay.