We purchased tickets from US to Nepal via Qatar airlines. We got the tickets with my wife's old passport which had her maiden name. Recently, we applied for new passport with updated name. We didn't know the potential hassle involved with this change. We need to get new tickets issued for her and it is very expensive. Does anyone know of people's experience when they travel with different names on passport and tickets? We will take old passport copy & marriage certificate as well. Is there hassle in that? Airlines have said they will put a note for their agents but we will be travelling at our own risk. Also they said immigration is another issue altogether.

You need to get your name fixed in ticket. I don't think you will be able to travel.

Your first effort should be checking with the ticket issuer.
If she has both surnames , it may be considered.