This from Wikipedia:
"The USO was founded in 1941 in response to a request from President Franklin D. Roosevelt to provide morale and recreation services to U.S. uniformed military personnel. Roosevelt was elected as its honorary chairman. This request brought together six civilian organizations: the Salvation Army, Young Men’s Christian Association (YMCA), Young Women’s Christian Association (YWCA), National Catholic Community Service, National Travelers Aid Association and the National Jewish Welfare Board. They were brought together under one umbrella to support U.S. troops. Roosevelt said he wanted "these private organizations to handle the on-leave recreation of the men in the armed forces." According to historian Emily Yellin, "The government was to build the buildings and the USO was to raise private funds to carry out its main mission: boosting the morale of the military.""
So your best bet is to contact the above organizations local to the area your ancestor lived to see if they have an archive of Volunteers and records of personnel for the WWII years. The "service women" you refer too were mostly Volunteers who showed up as they could. They were not paid or employed unless they were already staff of the above organizations as events were planned ad held. None were to this day connected to the Federal Government for them to "keep records".
You might look at historical newspapers of the areas the USO was located for pictures and which organization took on the USO events. Also contact the local city or county Historical Society or Genealogical Society for "yearbooks" if they exists.