What happens once isn't the same all the time.
Different priced tickets all have a sliding scales of charges.
On top of that the biggest factor will always be availability. There are about 15 different fare classes in economy alone. If the class she has booked isn't available on the new date she will have to pay the fare difference on top of the change fee. At last minute that will almost always cost a shed load unless a very quiet time of the year, which this isn't. This is the 2nd busiest.
So AA sounds like the normal process. Not sure what Expedia is doing, but sounds dodgy.. Always best to book direct withy the airline as the price is usually very similar and then you get the easiest way of changing tickets. It is sometimes very hard to change a changed able ticket bought from an agent.