Yes You can.

It is called as Return Permit for Exceeded Time Period.

1) Your wife's RP should still be valid.
2)Go to the immigration office located outside airport and give them the copy of your wife's passport and tell them you need to extend the reentry beyond 6 months. You have to pay QR500 and they will give you a receipt for it. Send the copy of this receipt to your wife just for ref. System gets updated and yoru wife should not have any problem returning within 12 months.

I have done this for my wife 3 years back and I don't think the rules have changed.

Check on the following link in Hukoomi website and just clarify with immigration officials on the validity of such permits.

http://portal.www.gov.qa/wps/portal/!ut/p/c1/04_SB8K8xLLM9MSSzPy8xBz9CP0...