Take the Mrs' new and old passport if she still has it. Also take your wedding certificate and deed poll (if applicable). They shouldn't give you much grief if you present all three together. Just make sure to be at the airport on time so you don't hold up a long queue 1 hour before departure.

Usually the airline will be happy with this and not charge you a name change fee. Don't pay a name change fee, it is supposed to apply when the person named on the ticket changes, not when the person named on the ticket changes her name. Been there a couple of times with the Mrs and it was fine.