I think it depends on what passport she holds, my wife arrives in a week, and I have booked her the Al Maha service from the airport. It was 110QR for the Al Maha service and 100QR for the visa. My wife hold a UK passport, so I dont know if it would be different for someone with a different Nationality.

You could always go to the Arrivals at the airport, on the far right hand side, just before Costa Coffee. That is where the Al Maha desk is, they will be able to tell you there and then.

Hope this helps.