True, you can get the passport very quickly if you pay the fee for expedited service.
Yeah, you can just buy the plane tickets in her maiden name and fly with the current passport.
Actually, I wonder if you would have a problem flying back since the new passport name would not match the name in the round-trip ticket, or vice versa. For myself, I wouldn't risk it, I will just book the ticket in her maiden name and fly with her old passport.