Want to go to Disney; Southwest is giving me a hard time.?

I ordered some plane tickets on the wanna get away fare with Southwest Airlines. I wanted to take my "play" mother (a person that is not my blood mother that I look to as a parent) with me to Walt Disney World in Orlando. She has never been there ever in her life. Now she cannot take off work for whatever the reason is. I called Southwest ONCE, and the operator told me that I cannot change the name on the ticket. My nephew who is eight has never been to Disney World. It would be nice to take him in her place. How can I get Southwest to change their mind? I don't want to change any flight or anything, I just need to change the name on the ticket. If I can't I will be out of almost $250 dollars. I want my nephew's Disney's trip to become a reality. Can someone give me help or make a suggestion?