flipforfun: you could also try a local tv station that offers consumer help - like in California on channel ABC we have "Finney on Your Side".
BBB also good option. Their web is
http://www.bbb.org .
If she didn't already cash the checks, you could cancel them, or if it was paid by credit card, maybe you could canel that.
According to the Dallas Gymnastics web, she's going to The Gymnastics Place gym, so you could also go there and confront her if you would like...or try the other options.