Before exiting the airport there are several companies with counters facing the exit. These are the companies that charge INR 1,600 incl toll. If I choose one of these companies I select one with minimal waiting time.

The Airport taxis are on the left hand side after exiting the airport. There is a single queue for 2 companies providing AC taxis.

Both of the above are easy to locate and staff will assist if your wife is not sure where to go. I have never had a problem with taxi drivers coming from the airport, neither with taxi or rickshaw drivers in the city.

Another option is to get a hotel pick up, which will probably cost more.