Fees for Southwest flight changes?

[Pooh's Pal]

My boss made her December reservations via the Phone to Southwest (she has a toddler traveling with her) the day Southwest released thier December flight times and rates. Now she may have to change her return date and was wondering, if so how much?
Will she pay just a fee(say $50 per ticket change) or just the difference in the price of the flight per ticket? or both?

Any info would be helpful!
Thanks in advance!

 

[lawgs]

no flight ticket change cost......but if the new date/flight has a higher fare she will have to pay the difference