Arrange for the following documents for visit visa of your wife.
1. NOC from your company.
2. Marriage certificate attested by the immigration dept in Qatar.
3. Passport copy of you & your wife.
4. Copy of Your ID, your company's ID showing the name & signatures of your sponsor.
5. Salary certificate showing your designation and salary.(Preferably showing Housing allowance also as u will be shifting to personal accomodation after her arrival)

Kindly check with your PRO if any additional docs are required. Charges are nominal between QAR.120-200. For extension to further six month, theres a per month fees of QAR. 200/-

Submit all these documents and check the status online after 3 days. Once she arrives in Qatar, after the medical formalities she can stay here for maximum 6 months (further extention up to 15 days). Dont bring her on tourist visa as it will be only for short stay.

Hope u will find this information useful. Wish you all the best.