The group she got to represent is called The Greater New Orleans Therapeutic Riding Center (as you can see on the banner they display in the parade). It is a great non-profit organization that goes by the theory that riding a horse helps build a certain confidence in handicapped children that they may not be able to get elsewhere... I also must mention the exercise it provides to children with the inability to walk.
As you can see, she got to ride up front behind the banner, and she's the only one representing the organization... Is that because she's the best rider they have? Probably.